I have the PC version and the paid web version, so the main benefit there is that you can sync the two. I REALLY like that for when I'm not at my main computer but don't want to forget to enter something, or if I forget how many cals I have left in my day. The only (but big, IMO) drawback to the web version, both free and paid, is that you can't create a recipe! What?? You can do that on the web version, and the recipe STATS will sync to the web version, but you can't edit the recipe on the web version.
I hope that helps somewhat. I've tried lots of nutrition programs over the years and overall I like FitDay bets because of the ability to use a PC and the web. So, if my computer is in the shop,I can't go "oh, well, I might as well pig out since I can't track it anyway"...same for if the internet is down.