Haha...my two late yearlings are definitely "lazy"...I swear they are broken!! The filly can be more energetic, and that makes training relatively easy, because I know what she's 'thinking', or rather, that she IS thinking. The boy is always calm, until he decides to blow up...granted, he doesn't do that often (I think it would take too much energy on his part...LOL), but you can't see it coming, because it just happens. I PREFER a horse like his sister, or my mare, where you can see the thinking process happening, because you're actually getting some kind of response...and when you get a reaction, you know what you need to work on, and you know to step back a bit, so you CAN work on what they are uncomfortable with. With a super lazy horse, they may not like something, but you don't know it, until he becomes so uncomfortable that he blows up. Think "Jekyll and Hyde"...
As far as how to tell what kind of energy your horse has, there is no 'table of horse energy'...either he's energetic, or he's not; and there is alot of in between. I prefer some amount of energy, even the fiery kind, because I know the reaction will come, and I can work through whatever it is they are reacting too; with those horses that have little or no 'energetic' side to them, you may either never have reactions, or they will come and take you totally off guard; which to me, makes those sort of horses much more dangerous than those who are energetic. Er, from a trainers perspective that is.