Hi, I need your opinion..

Situation:
-currently i'm using crappy L7 TM router for Unifi 30Mbps..
-now got approximately 15-16 wifi devices (phone, laptop, PC, ipad, TV & smartbox) that connected to my router..
-but not all devices connected at the same time..
-only 10-12 devices connected at the same time..

Requirement:
-stable wifi signal for 15 devices connected simultaneously..
-strong wifi signal for 2 storey house..
-able to set guest wifi SSID (need to set max download speed)..
-QoS is a bonus..

can you suggest me which one of these routers RB951G-2HnD or RB750GL?? Thanks