I've done a stint at Jillian Michaels and then also at Daily Plate, but probably for the same reasons as a lot of people, I've switched to My Fitness Pal (myfitnespal.com)
1. The website tools are just better - Finding foods and adding to your diary are so much easier than the other two sites.
2. The apps are better. To be fair, the only app I can compare to is Daily Plate, but it was horrible. I find the Android version of MFP better than the iOS, but I have both.
3. The support is better. Due to a hectic work schedule I hadn't logged in for 3 days and one of my MFP friends emailed me to check up on me. Anywhere else no one would have noticed.
4. It's FREE. Yes, just as much support and it's free.
Of course you get as much out as you put into it, but for my money (and there isn't any involved here) MFP is the best.