I have both the samsung s4, and the s5. the worst lag seems to be when trying to open the samsung email client -- the blue circle spins for a full 5-6 seconds as opposed to the s4, which instantly shows the emails. This is also true when opening certain emails (even if they are just a line or two) where once again, when I press both phones simultaneously, the s5 finally ones the email up to 2 seconds later than the S4... I have done all the suggested fixes found on forums (stopped animations, etc. etc.) No difference. I changed to Nova Launcher, still absolutely no improvement on that Samsung email client. I finally called Samsung technical support. He made me do a few more things, but still no improvement... Then, I asked him to try opening the S5 Samsung email app himself, simultaneously to the S4... Guess what... SAME 5-6 second spinning blue disk for him as well (he hadn't experienced it before as he personally was still on the S4) He said he would file a report with the development team... I think Samsung is perfectly aware of the problem... As for those who say there is 0 lag, either you are one of the blessed ones, or perhaps you're simply less sensitive to it... Anyway, after much thought, I changed back to the S4... I am truly shocked that Samsung could release a product that clearly huge numbers of people and articles identify as "lagging" (i.e. not opening up as quickly as they should)...