Well, at the moment the balance is.. unfinished, so it's hard to predict what will be good choices in the end. Great warriors is a good example, it basically doubles the combat speed of trained units (can't remember if it affects sovereign/champions), but at such a cost you can't get much else - it's hard to fit in, but if you do no one's going to be able to match you with a standard military. Not that it matters when your sovereign can stomp the AIs singlehandedly, but hypothetically speaking, it would be far too powerful if you were otherwise evenly matched with your enemies. Weapon masters on the other hand is useless, it gives you access to an overpriced sword that's not really better than far cheaper ones you can get through research. Meanwhile armor master gives you an overpowered/bugged breastplate that's significantly better than heavy plate and free for units you train (also available to sovereign/champions at significant but worthwhile cost). Really too early to judge these abilities, until a few more iterations of balance and bug fixing.
