Cobblestone – cheap and cheerful stuff, blast radius depends on gunpowder but is as standard pretty low. Can (if lucky) one shot people in diamond armour. Best choice (and more or less only choice) for ships.

TNT – Very large blast radius, blows up on contact with a surface, and drops 2-3 more tnt which then explode leaving a lot of holes about. Does a lot of damage, over a large area.

Fireworks – Large blast radius, high damage radius, used to a lot in sieges. Has the best penetration damage (roughly 3-4 blocks). Doesn’t do much else. Only works for normal rockets without effects.

Melon seeds – Its a shotgun. Close range it devistates by launching between 8-12 single ‘shots’ that do roughly 2-3 hearts of damage depending on armor worn. However over medium to long distances it becomes less effective, becoming pretty much pointless beyond 50 blocks

No difference in trajectory though – that depends on gunpowder and cannon angle. Fireworks, TNT, and cobblestone all have a ‘single’ initial projectile, whereas melon seeds have many.