Crossfit is pretty  much just circuit training. It's been around for decades. But it's executed in one of the worst ways imaginable and invariably leads to injuries. It also comes with tons of unfounded baggage like Paleo dieting and the like.  I'm not too familiar with P90X, it seems like a pretty standard cross-training home routine. I haven't heard of it producing a bunch of injuries. It's probably good for your average non-lifter to get some exercise in and build up strength but you won't see much in the way of results after a year or so doing it.  Crossfit is good if your goal is to A. Boost your ego, B. Pay a bunch of money, and C. Get hurt.  If you want to actually get stronger and look better just stick to a fundamentals-based training routine like one from here.