I have tried both programs and I am personally more drawn to Crossfit. Both P90X and Crossfit can be incredibly challenging if you really push yourself. I enjoy Crossfit more for a few reasons:
Working out in groups of highly motivated and intense individuals increases pressure, accountability and engagement.
The instructors I have worked with are highly skilled and can help you improve your lifting form.
Driving to the gym provides apt physical and mental separation from my place of rest whereas working out at home can be easier to push aside or delay.
High level muscle confusion: both P90X and Crossfit target a variety of muscle groups and use varied exercise techniques to keep the body evolving at a high rate. After doing P90X for some time, you begin to anticipate everything from the exercises to the words Tony says, which can lead to adaptation and sometimes boredom. I don’t know what Crossfit workout I am going to do until I get to the gym.
One of the most important factors is the inclusion of what I like to call the “Ancient Lifts” (squat, deadlift, clean and press, snatch, bench). It is hard to do these in your apartment, much less without the proper equipment.
Lastly, instead of looking at these programs as competitors, I like to use them in conjunction. A proper Crossfit routine can take a lot out of you, so you can train at home using P90X in your off days. This way, you are getting the best of both worlds.
In regards to the target audience for P90X and Crossfit, it is hard to determine which program is right for you until you do ample research, and perhaps try them both (you can find a variety of example videos on YouTube and the Crossfit website). P90X allows you to work at your own pace from the comfort of your home, but requires an investment in equipment and instructional DVDs. Crossfit requires that you have a sufficient working knowledge of the plethora of exercises and live near a gym with a Crossfit program. I think that P90X is excellent training for Crossfit, but feel that Crossfit will produce a more complete physique and lift portfolio. I have enormous respect for anyone who attempts either program, and find that in the end it is just important to push yourself.
If you are in the Salt Lake City area and want to try CrossFit, head over for Factum CrossFit and Mixed Martial Arts in Sandy, UT.
Disclaimer: Consult a physician before taking advice from anyone on the internet, do significant research on both programs, know your body and start slowly (focusing on form) and increase the weight after you know what you are doing.