IncTeh: Here's the update:
I went back to Challenger and told them the incorrect suggestion of the salesman and they instantly gave me back the in-store credit refund, so I had $160 to spend again.
The guy in the customer service told me to look for a particular salesman because of his 'expertise' in networking to find the right one.
I talked to the new rep and he suggested the Asus RT-AC66 but warned me that it'd still depend on which Starhub subscription I'm on because of
*unfortunately, he lost me when he started talking networking jargon hehe*...
Anyway, I said I was on the 50Mbps basic fiber plan and not sure about the other specs he was asking.
He asked me again what my main issue was (speed, range, compatibility, etc.) and I said I just want to have more signal in the farthest bedroom and speed wasn't a priority because we don't do heavy surfing/DL/etc. in the bedroom.
He then suggested that I just pick up a WiFi extender, specifically the Cisco/Linksys RE1000 because that's the model that doesn't drop the speed by half compared to the other models.
So that's what I did.
It worked pretty well, to be honest. In the bedroom, I normally get 1 to zero bars on my Galaxy Note with the door closed.
Right now, with the extender, I'm on full-bars. Speedtest.net is still showing around 35-40mbps DL speed in the bedroom.
My results are pretty much the same as this guy:
Linksys RE1000 Wireless-N Range Extender Review - YouTube
Not sure what negatives I may be experiencing now, but I'm too ignorant to know LOL.
Still, I can't thank you enough for the help. Much rep!