Both apps listed above are very good. I use Lose it! On my phone because I can literally scan the barcode of a product and it puts it into my calories for the day (once you say how much you had) which is much more precise than when some say: Cookies- general etc.
However, I use my Fitness Pal online, because it has great forums and groups for support and you can ask questions and find people doing the same excersise routine as you. For example, I am doing the 30 day shred video, and there is a group for that.
Both are good, it just depends on taste.