I have to choose an engine for a 3d stratey game Whats the best 3d engine for you? I mean the more complete and well documented

Your own.

I agree with RickQ. You should write your own engine.

you SHOULD program your own engine, but if time doesn''t permit, get the tribes2 engine, it has good landscape support, and you can license it for 100$. But again, if you''re not making a commercial game, write your own engine.