To be honest, I'm not quite a fan of TouchWiz, but Samsung devices seem to be the best for me (at least in custom ROM support...). I'm quite happy with the S5 but I don't know which phone will I buy next time... maybe a Nexus or a OnePlus One
Well, my first Android phone was a S3, but before that I bought in 2010 a chinese tablet with Android 2.1... and trust me, I have friends who bought chinese tablets last year and... wow, they have improved a lot...
Android and iOS graphic performance
In an AppleInsider article about the graphic comparison between the iPhone and different android phones, the writter clearly stated that the reason why this happened was due to Android, and not due to the hardware they used. He said it was the platform itself...