(Got some free time so I´m gonna check/improve the cannon parts. I´m kinda lazy so please don´t expect too much.)
The standard cannon has pros and cons.
pros: high dps (damage per second), doesn't use alot of ammo, doesn't use alot of energy, but can penetrate blocks.
cons: volatile, needs ammo to shoot, takes more space than the laser.
The standard cannon has a shorter range than the large cannon and deals less damage but needs much less ammo to shoot, In fact you can run 2 standard cannons on 1 ammo factory and they will keep shooting.
Standard cannons can be used as the ships main dmg source but they are weak against shields. Standard cannons explode when destroyed.
The large cannon is quite like the standard cannon and needs ammo to shoot, but unlike the standard cannon, the large cannon needs a lot more ammo, you should use about 1.5 ammo factorys per large cannon. While not shooting fast, every shoot will do high damage and can penetrate a few layers. The large cannon has a long range and will usually start shooting first, but its shells are slow and will take some time to get to their taget. Large cannons explode when destroyed.
(PS: English isn´t my first language neither so there might be some mistakes, but please be considerate.)