It is purely unit abilities that matter, and the bonuses that certain generals have when they are a certain unit type. Generally speaking if you are playing temple, the personal guard path is best for defense, and the elite black rider is the best dps unit. This is not always the case depending on the general, but certain units are just plain bad. Corsair's for example are very good for pvp, but in the pve content they are pretty worthless, since your opponents always have far more life. Archers are also very strong if you have master strategist or other generals that get a large bonus from the class. Ninjas are almost always worthless, unless you have a 4 star oni hanzo or something at least, and even then it isn't the best general.