Are rogues useful?

[Pyros]

Is it better to go with a ranged rogue (basically maxing out only missile weapons, the rest is useless to that king of gameplay) or with an assassination/dagger rogue considering they both stay in the back row?

Better with missile(or even throwing weapons). Backline melee rogue is meh, mostly because it relies heavily on backstab to do damage, which aren't easy to get off in many situations. Maybe you're fighting in a corridor, maybe you're fighting in a doorway because there's many mobs, and even in a large room maneuvering for backstabs is quite a lot of work and puts you at a potential risk. It's doable, but compared to ranged attacks I don't really think it's worth it, unless you really want backstabs(in this case it's fine, don't need to minmax to finish the game at least on normal).

[gasgas]

Indeed, I have just restarted with a new party and a missile weapons only rogue, double hit is insane, I am at level 9 now and basically a ranged rogue can out-dps anything.