I've had an iPhone 4s then 5s and upgraded to a GS6 a few weeks ago. After 4 days I got very close to returning it and waiting for the 6s but glad I didn't. My main issue was poor battery life, but after persistence there were 2 primary causes of the drain, the first and biggest was Google Nows location tracking feature, I have GPS location enabled and drive around most of the day, as soon as I disabled this feature the battery life gained hours. The second was screen brightness, I had it noticeably brighter than my 5s and had to turn it down a lot to match it. Something to be aware of is amoled screens light each pixel and theres a hell of a lot of pixels in these devices, the same as a high quality 27" monitor! The brighter the screen the more power it sucks, this could explain the irregular power use some are seeing, e.g. Facebook with a lot of white pixels will use more power than a dark scene within a film. I also had a lot of stuttering, especially on this site, but since clearing my Chrome cache things seem a lot smoother. The memory leaks of 5.0.2 is my only real complaint now, almost every web page needs to refresh when switching between tabs which is really annoying, hopefully 5.1.1 will help when my network eventually releases it. I also didn't like touch wiz, not sure if it was the animations or something else, however Nova launchers superb and solved that issue completely. Loving it now, wouldn't go back unless the 6S has something very special.