Where you can find good units paladin?

[Keneth]

The stuff you pick off the floor is mostly useless, except maybe thorn sprouts at the very beginning and later on dragon eggs. The ent roots or whatever they're called are also worth considering.

You should note that almost all units in the game are random and you might get them later than you might want or not at all. As for which are the best to have, you should read up on several threads regarding unit comparison and suggestions.