I've only had the iPhone, so I can only give you my experience with it and not any others.
The app works splendidly. I've got it set up right on the first page of my phone, so I just tap it open and log in my food/exercise/ghg/what-have-you. No problems.
I only have experience with the iphone (and an ipod touch before that) as well. I love having it at my fingertips at any point throughout the day.
Very easy to work with!
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The road to success is dotted with many tempting parking places. ~ Unknown
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I use the WW app on my android phone and also use it on the ipad.
Biggest difference are the number of "features". That said, I'm not sure if the ipad and iphone apps are exactly the same, if they are, then I might like the iphone app better than droid app. All in all, both android app and ipad app do fine with tracking, logging points etc.
I have an Android App So far i like it.. I logged on to my pc and made some changes and wanted to see if it was made available on the app and it was there like immediately which is good!
One thing that I am having trouble with is searching for foods.. for example on my PC i can put in Greek Yogurt and choose to look for a brand name (IE: Chobani) But on my App I can't seem to do that.. sigh.. HELP! maybe i'm doing it wrong?
I have the iPhone app. The only thing I dont like about it is that you cant input your own recipe to calculate the points. It's a bit annoying when you make a big stew or soup or casserole and you cant work out how many points are in each portion.