I had an s4 and switched to the G2. Went back to my s4 BC I missed it. Now have the s5 and wouldn't go back to LG. I like the high saturated display on the s5 and just feel that Samsung is overall a better interface with better features. If you are really used to Samsung touchwiz and like it, I wouldn't go to the g3 but your call
Do it g3 is newer and better in many ways.Well, TouchWiz isn't that big a deal to me, I use the Nova launcher and SwiftKey.