To expand on Motorep's excellent comments:
It really does not matter as both are sports, so accordingly do not really offer the stress of interpersonal gunfighting.
The practicality and tactical soundness of the stages vary more from club to club than one would think. Yes, IDPA should be a little better.
But, let me say it again, just go ahead and do it. Doing it is better than not. It is that simple, try them both, then specialize if you've a mind to. But DO IT AS SOON AS YOU CAN!
Ni ellegimit carborundum esse!
Yours In Marksmanship