You need to ask?
The better answer is...why not? We're humans; we might as well!
But before we begin, I'll first state that this is under a few assumptions:
-It's the future.
-Humanity advanced on its own, without outside influence.
-Humanity has made contact with at least one, if not multiple, alien races, and communication between them has been made easily possible.
-The aliens in question are similar enough to us for comparisons to be made, but different enough to not be rubber-forehead aliens.
-As a result, expect some similarities: tech approximately equal to our own, but in some areas more advanced and in others more basic; cultural diversity similar to what we have on Earth, but distinctly different; biology that makes sense from their home planet yet which allows for them to still operate on some of the basic systems we do (for instance, beings vaguely resembling space mammals, reptiles, insects, plants, and maybe starfish/squid/so on are perfectly fine, but literal gray goo of an alien is not, at least for the purposes of THIS spaceship); language communication that is comparable to our own (sights, sounds, thoughts).
-Humanity is not unified, but there is a dominant faction of humanity that generally represents the majority of people, and while flawed, is still loosely similar to some of the democratic governments we have now.
Basically, quite a bit like Stargate SG-1 with a side of StarCraft thrown in and Star Wars on the side. (Star Trek, not so much.)
Let's start with my favorite subject: weapons. The ship I'm building is not meant purely for combat, but is certainly not defenseless. A general-purpose vessel, probably called a 'Cruiser' because that seems to be a good fit (at least to the sci-fi description of a Cruiser) to what I have in mind.
So it's going to be fairly large. Assuming space combat is a thing in this setting (and why the weapons if not?), it'd be logical to think that it wouldn't be just two large vessels pummeling away at each other. (Thus, not the majority of Star Trek. As the franchise went on, it did get better about this, and to be fair, ships in Star Trek are very versatile with their movement speed, shield strength, and weapon banks, butstill, this ship has more in common with Galactica than Enterprise.)
You'd have fighters flying about. So to counter the fighters, you'd want weapon banks across the ship, able to defend it from every angle, with cross-coverage so that an enemy fighter can be hit by at least two or three different guns. The guns would be computer-guided, but with the ability to be piloted/manually overridden by a human, because human instinct generally trumps computer logic in battle, especially if the human is still using the aid of the computer. (Computer + human > just a human > just a computer generally for this kind of thing, because no matter how advanced the computer system, if fighting a human or humanlike opponent, the computer simply can't predict and counter enemy movements as efficiently as a human can.)
What would the guns actually be, though? Well, that depends. See, when it comes to vessels, there's limitations off of power and size. You can have speed, maneuverability, firepower, and defensive capacities; you can even have more than one. Fighters would focus on speed and maneuverability. But you can't have all of them at once, so the fighters would either sacrifice firepower or defense. Given that these are fighters, attacking an enemy vessel, presumably they give up defense.
In that case, the guns can be good ol' projectile weapons. I imagine that they'll stay just as relevant in the future as they are now. I wouldn't call them 'machine guns', because that implies something too small. I don't remember what their name would be, but we've had high-caliber rapid-fire projectile weapons for decades, things that put a 50 cal to shame in fact, and I think that something as simple as that would absolutely shred an enemy fighter. No need for wasting a bunch of energy for energy weapons if the enemy fighters can be pulverized by some good ol' lead.
However, were the fighters in question meant mostly to be more defensive vessels, sacrificing attack for some sort of protection (be it heavy armor plating of some futuristic kind or some personal shielding that stops projectile weapons dead), then by necessity you'd have to use whatever the energized weapons would be called. Ion cannons, plasma guns, whatever. I imagine they probably wouldn't be as steady in their stream of fire as the projectiles, but that's not necessarily a bad thing; we already fire projectiles in bursts anyway, not constantly streaming fire in all directions. However, I do think that whatever these small guns would be, they would still fire a bunch of rapid bursts, like a projectile, the only difference being their composition.
A logical progression from having smart guns defending the ship (let's call them the "point-defense system" because that sounds science-fictioney) would be to have small missiles. We already have small, smart missiles that can track a target they're locked onto, and again, have had variants of this tech for decades. The future would be no different, and could have it work as an additional method of defense. I'm not sure whether it'd be smarter to have the computer be tied to the point-defense system or separate, but having a full load of small missiles carrying explosive ordinance to obliterate incoming fighters sounds like a smart idea to me.
Naturally, there would be different payloads as needed, and they wouldn't work as well against a larger vessel (larger vessels likely having an equivalent to the point-defense system to shoot down said missiles and having the defenses strong enough where even an impact to the ship doesn't do noticeable damage because the missile's too small and lacks the punch needed), but they'd be very handy to help defend.
That takes care of the smallfry. What do I envision a cruiser having for big guns? A small arsenal of larger missiles (think photon torpedoes, I guess), for a start, but not a huge one and not much variety. (This is a cruiser, not a battleship.) So here's where the big energy guns come in. Though obviously, the front of the ship is where the majority of the power would be, there would be guns positioned along the sides of the ship, so like with the point-defense system, the ships can fire from multiple angles, never truly being defenseless to enemy attack. I don't think on a cruiser, it'd be feasible to have this coverage be absolute (battleship, sure, but not a cruiser), but there would definitely be a spherical range, where if the weapons lock onto the target, they can fire and hit it.
For these big guns, the best way I can think of them to work is to impart as much energy into their attack as possible. The goal, of course, being to punch through the enemy vessel as much as possible. So a continuous stream would probably be best for this, for as long as the lock lasts and the command to fire is there.
That would be it for attack, aside from a small compliment of fighters, 4-12 in number. What would defense be? Well, I imagine a heavily-armored hull would be a good start. The hull could probably have some built-in properties depending on the metal that make it resistant to the type of weapons likely to hit it, too. Imagine an energy weapon hitting the hull, and the hull absorbing the energy to give the ship more power rather than destroying it--that's probably not going to happen, but imagine something like that in effect; instead of an energy weapon penetrating the hull and destroying the vessel, the energy weapon is dissipated.
This, incidentally, is how I see any energy shielding working (and what sci-fi setting is complete without energy shields?), in that rather than reducing the blow to nothingness, wasting a lot of energy by countering force with an equal and opposite force, is to simply redirect that energy, so that the incoming force is then spread out and weakened. It'd work with projectiles, too, in that it's more efficient to have, say, a bullet be directed not to hit you rather than just flattening the bullet before it does.
The exact mechanics of energy shielding largely depend on the exact mechanics of energy weapons, but while it does seem logical to have it be slightly-spherical (to make things be redirected the best), or more accurately an oval, the shield would likely be directly above the ship itself, because whatever has to generate the shield needs a lot less power the less distance it has to travel.
The cruiser would also have at least 2, if not 4, vessels that'd be shuttles, basically miniature cruisers without the weapons (aside from maybe one small frontal energy one) but with the defenses. The shuttles and the cruiser itself would have plenty of computers and scanners and whatnot, to basically be able to perform scientific studies, be on guard for enemies, whatever. I imagine that the shuttles would look somewhat like our current shuttles do, and be able of entering atmospheres, and they would therefore need powerful thrust to escape the atmosphere.
The cruiser itself, though, I don't see as being viable to land in most atmospheres, because of its massive weight--not a problem in space, but quite problematic when it comes to the harsh mistress of gravity and escape velocity. I do imagine it being shaped like the majority of ships in science-fiction, though: it would be fairly long, strong engines on back, wings, think Daedalus-class ships from SG-1.
Power and method of FTL travel depend on the setting, of course. (For that matter, if not rockets, what slower-than-light travel they use would be, too.) As does method of having gravity. But in a setting with contact with aliens, this is the type of ship I would build: versatile, able to respond to most situations and do so quickly and efficiently.