For those unaware, the ship classifications are as follows.
Dreadnoughts-Ship killers-Effective against all Space ships and generally have small crews.
Cruisers-These are generally large ships that primarily act for troop transport, but at the same time have some offensive and defensive capabilities. These are the jack of all trade ships.
Frigates- These are fairly small fast attack ships and are somewhat similar to corvettes, they act in support roles mostly.
Corvettes- these are generally used for anti-fighter combat, useful for taking out bombers which are superior against ships like Dreadnoughts.
Destroyers-Weaponry is based around attacking planets, and possibly space stations, little other use apart from this.