You haven't told us which internet package you are subscribed to, nor what assorted equipment is connected to your LAN, As a result we don't really have any idea which router would serve you the best. Tell us your networking needs and performance expectations.
Based on your previous thread it appears that devices work fine when direct connected to the modem, correct?
What happens when devices are direct connected to the router (not wifi)?
When you swap devices around from the modem and router are you rebooting everything...modem, then router, then device?
If you get your own router you can't really go wrong with the Asus RT-AC66U as @RAIST5150 suggested. The TP-link Archer A7 is usually very reliable as well. I wonder if you just got a bad one.