Ships & Modules

Better to train both or stick to one?

Stop at cruisers and that's mostly just for tengu for caldari unless you are going to be mission whoring and even then a tengu might be better because its not that long to train for and useful for more than missions when you grow bored of them(wich you will at some point). Might want to train for the caldari battleship rokh later if you decide to go gallente and/or hybrids.

So train heavy missiles and possibly heavy assault missiles and the missile support skills, you can leave all other missile skills alone really. I have torps and cruise 5 and they are almost never used,this was before tengu was introduced to the game
Might want rockets or light missiles if you do frigate pvp
Then go gunnery and another race or don't go caldari at all but the tengu is a beast for pve though.

Go check recruitment threads and see how many people are advertising for "shield and missile pilots" if you want proof. - all caldari ships are shield tanked and most have missile on them with a few having hybrid guns.

Hybrids opens up easier cross training into Projectiles and Lasers, and unlocks a decent portion of Gallente ships as well (with rudimentary drone skills). Missiles however unlocks a moderate portion of both the Caldari and Minmatar ships, as well as opening up one branch of Amarr T2 ships.

I'd say do as Lili Lu said, and train both to T1 and use the one you liked most.

But honestly, if you're running missions I'd say just go projectiles. PvP do whatever you want.

Train for t2 medium hybrids, lml's, hml's and HAM's.

And then just train for large hybrids. Even though torps have their value that is mainly in pantheon fleets and such which most likely you don't have to worry about.

All races have two weapon systems, if you want fly all your ships then train both. Training both will give you a lot more versatility.

As already suggested try out both and see what you prefer.

Missiles have flight time but their damage application is only calculated by the enemy signature and speed, so they ignore normal gun tracking. Hybrids (and guns in general) required you to reduce transversal so your guns can track the enemy, but does instantaneous damage and can do wrecking shots for increased damage (only like 1% chance for 300% damage). Optimal and Falloff is important for guns while missiles only have velocity*speed as their range.

I would favor guns because the support skills you train goes across to projectiles and lasers, and most pvp fleets seems to favor this as well (except the Drake / Tengu blobs). Missiles are still viable though, but they work a bit differently and currently the cruise/torpedo missiles need a bit of rework in most peoples eyes.

Remember this is EVE and you can train both. Whether you choose to focus on one first and decide to get the other one afterwards (or at all) or skill them both up simultaneously is all up to you. Just remember each weapon system has good and bad sides, and it is a bit of a personal preference what you prefer.