Neutral ships are used to help balance the weakness of the different classes in gc. For instance terran ships in general are weak to chemical so throw in some fezz or kings and queens once in awhile and you have a good chance of winning.
Guards typically are weak to missile so throw in some fezz to mix it up
Using c.class on defence is a smart choice and the high hull is great against queens and runners. Aries for example is slow and expensive but the hull to pr ratio is 4-1 its the best in the game.
Broad sword is mostly for offence (depends on play style) and sword is for defence.
Try to think of your fleet in terms of offence or defence, are you going out to attack or are you building to defend against someone above you. In gc you have to know how ships interact in battle at the different attitude`s to understand why each ship may or may not be useful in a givin situation.