Hey, I'll do a side by side comparison so you can see why I decide what I decide.
It does end up having slightly more defense, with a total stat of 450.
It has the same typing as Alakazam.
It has slightly less defense than Kadabra, but much more offense with 500.
It has the same typing
It has a mega evolution (if you want to use your mega on him)
It is pretty obvious who obvious who is better if you look at their stats, Kadabra ends up having 5 more Sp. Def and the same Defense as Alakazam. Alakazam has so much more stats than Kadabra that he is obviously the better choice.
Hope I helped!