Kadabra is better
If you are near the end of the game, and need coverage.
Also, I'm assuming this in in-game, so I take it that abilities and EV's/IV's and natures wont matter?
-Energy Ball/Calm Mind
How to get these moves:
-Shadow Ball can be found at route 210 after obtaining rock smash.
-Psychic can be found at route 211 after getting rock climb, or can be learnt at level 40.
-Energy Ball can be found at route 226/ Calm Mind can be bought at Battle Tower.
-Signal Beam can be learnt by the Move Tutor/ Recover is learnt via level 30.
Chimecho is better
If you are near the beginning of the game, and just need a Psychic type.
Well, he is pretty much a mini-dabra to compensate.
(Pretty much the same as Kadabras...)