At what rssi/dBm value does a new smartphone(S6/iPhone6) has a good wifi connection? Anything changed compared to old ones?
-72 or better will give you a good connection. Apple says that at -72 the iPhone starts looking to roam.
> -55 = best signal highest MCS rate
-56-65 Very good signal medium MCS rates
-65-75 Weak signal lower MCS rates
-76-86 very weak signal expect BPSK