Conclusion:[U]

1) If you don't care or never going to use the IPTV provided, TP-Link would be good enough. Relatively cheaper yet decent with good signal strength.
2) If you are watching the IPTV, please avoid TP-Link and get an Asus.

Full story here. [U]
I live in a double storey terrace house. The router provided by Unifi not strong enough to cover the first floor. So I decided to get a new router on my own.

First, I bought TP-Link WR841HP. The signal strength is good. Good enough to cover every corner of my house (both ground and first floor) with stable wifi connection. But the problem is, even though it's Unifi compatible, it doesn't seem to support IPTV. Some channels can only be viewed for like 5 mins then the screen goes completely off without connection. Other channels only show black screen. In short, non of the channels are actually working.

So I called up for Unifi support (I spent 5 days just to lodged a report. On the fifth day it took me 3.5 hours non stop calling and waiting on the line just to speak to a manager. A very frustrating experience). Then after bloody 2 weeks time of waiting, I managed to talk to an Unifi field technician.
His explanation is short and simple. Get an Asus router.

So I bought Asus RT-N12HP. After using for two days, so far so good.
Wifi connection strong and stable. IPTV works perfectly fine.