first i know its wrong section and this will be likely closed rather than moved but anyway.
installing a rom is you choice, i dont have the s5, but if i had i would do so, dude on this soc, this thing lags while scrolling lists and changing homescreens (wtf?) and animations are normally choppy (i used one for about a week). also i dont like touchwiz ui, for me, touchwiz only in note series.(but i would keep in mind a custom stock, since some features are usefull, and the camera app is really good)