I think it depends on what your goals are. Yes, P90X is predominately a strength program, but that doesn't mean that you won't burn fat by doing it. Insanity is a cardio program at its core and utilizes body weight exercise for strength work. If you have knee issues, it might not be the best choice for you since there is A LOT of jumping involved.
I love Insanity (I prefer sports drills to dance-y workouts). I haven't tried P90X yet--it's on my want list for when I lose enough weight to even have a reasonable shot at doing a pull-up
I'm currently doing ChaLean Extreme (another strength program produced by BeachBody).
I think it depends a lot on your style and what you'll
enjoy doing--if you don't enjoy it, you'll be less likely to stick with it.
I would research both programs--check out the website, watch the clips. Since you like Turbo Jam, you might take a look at Turbo Fire (another BeachBody program). It's Chalene Johnson's latest program and is very intense..and a lotta fun
Good luck!