I use Lose It! (because that's the tracker I stumbled across first in the app store) and I am bery happy with it. I do admit that MyFitnessPal has many more items in its nutritional database so I will sometimes search through that and then add it to my Lose It! tracker if I need to.

I would compare their databases to see which have the foods and exercise you most frequently eat or do to see which would work best for you.

I'm on those sites, but I never use them. Color me embarrassed, lol.
I did notice that I ate a lot better when I kept my own food journal, it really does help keep you accountable.

I just never stick to anything.

For my android I have an app called Calorie Counter by fat secret. You can do it all from your phone or you can log in at home and it is all synced to your account. I haven't come across anything that is not in the database. It is stocked full of everything. If using your phone you can even scan the bar code and it is tallied up for you.

I really like it because it has a daily calendar that shows all of your totals of both food and exercise.

I haven't messed with any of the other sites to compare, but I LOVE this one...

I use fatsecret and like it. The database is pretty extensive, and I just like the site formatting better than myfitnesspal. The database isn't AS big as myfitnesspal, but I don't find it takes very long to find something online and add it to fatsecret's database whenever this does happen (which isn't very often).

I used fat secret and lost weight. It helps keep you accountable and you can add your foods to the database. I'm not using it now because I'm using body media.