I like swingbyswing, the issue I am having with it is that I find if my friend scores me, even with my name linked by email, it doesn't update my stats, so then all of us have to score every round.
Another app which is fun called "fantasygolfApp" or the free version is "fantasygolfAppLite" which is good because only one person needs to score and then not only does it update everyones stats but you can also see yours and you friends stats on your phone. Note that this isn't a normal golf scoring app, my friends and I just found it. It gives you points for fairway hits, greens in reg, you lose points for bunkers and stuff like that, it's pretty fun..