You might be able to judge based on general performance...
Evo has a what.. 1GHz processor, but the older kind (Snapdragon I think?), was the first of the big screens though. So based on that.. I don't, third or fourth generation Android? DroidX being one 'generation' beyond that.
But, Obscure is correct, since the makers are rolling out devices so quickly, it is hard to nail down a 'generation' like one would for other things.