I had a similar experience with my zoom modem that was supported by Cox on paper but in practice. I eventually ended up buying a new ASUS modem that had a way shorter boot up time than the one provided by Cox, with the exception of infrequent unscheduled and unexplained outages only recently in the last year, I've not had any issues.
Unfortunately there's no real way to test which router works best with which companies. The best way I found is buy a new modem check to see if it works, if it does not return it and exchange for a different modem and repeat.
Typically, higher quality routers and modems have less issues than lower quality ones but it comes at a price. Gauge what you need knowing that it is the backbone of your service experience and how often you believe your isp updates their equipment.