I'm currently using MyFitnessPal, not because it's particularly good or user-friendly, but because it's the most-downloaded one in the app store. That is relevant because you can scan barcodes with it and it'll automatically add the product's nutrition facts, and I think most of these are added by the community, rather than the people who manage the app.

Edit, forgot to add: I use the free version, which has ads and doesn't have a few advanced features like tracking micronutrients and some other stuff which I don't really care much about.