I don't think stats matter, its only a matter of moves, really, in general, unevolved Pokemon learn moves faster ( like if the evolved Pokemon learns the move X at level 50 then the unevolved learns it >50, like 40 or something ) However some Pokemon learn moves that the evolved form don't normally learn and vise versa, I don't know about Kadabra exactly, you need to check the moveset and then decide for youself.