One of my coworkers uses all three, and god, she's lost a TON of weight in just a few months, I think she goes down a pant size or two a month. I haven't used any of them, but once I get more space she said she'll let me use her copies... but she said TapOut of very tough, and so is P90X. She said p90X can get a little boring, and Insanity is more exciting.
Edit: My experiences with workout videos are the really old school Firm videos, and the Cher and Jane Fonda workouts, lol. Some of my earliest memories are working out with my mom. The Cindy Crawford workout is actually really good, and a bit more modern, but still only on VHS. For modern workout videos, I like Rodney Yee's yoga DVDs. You get get the Yoga Burn and Strength Building in a two pack for $10 or $15 at Target, or on
gaiam.com. I think they're really good, I can see tell I am getting stronger and a lot more flexible--if I go to touch my toes I can almost put my head right on the floor, but they're not cardio. I found modern Firm videos to be way too easy and not worth it (plus, they're girly), so I'd try either of the three you mentioned.