Buy Me A Pie! is supposed to be pretty good. It just came out for Android.
https://play.google.com/store/apps/d...buymeapie.bmap
I just use Wunderlist.
https://play.google.com/store/apps/d...derlistandroid
It works across Windows/Mac, iPad, iPhone, and Android. And so I have all these lists for like Starbucks, CVS, Wal-Mart, Target, etc.
I just put what the coupon is for, when it expires, and then I can check it off when I use it.
I have a pretty big wallet, and I keep my coupons in there. Having to have multiple apps for every store is such a PITA. And most places would rather you NOT use electronic coupons. Plus, it just makes the checkout slower. Just cut them out and keep them in a bag in your car.
As for which phone to get... Any of them will do. Just make sure it's affordable/doable for you beyond everything else. Neither iOS or Android work better when it comes to coupons. Although you could setup the Android phone to remind you when you're at certain GPS points to use a coupon.