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What's the best Modem and Router that I should select to meet COX requirement?
What tier/package do you pay for? See here for all Cox compatible modems and their maximum rated service. Also, did you have a budget in mind?
I have just upgraded to Ultimate Internet Service
around $200 would be ok for my purchase.
For the modem, I would go with the Arris SB6183. I have it myself and it's a very solid design for 65$. For the router, I am a fan of Asus. The model I would suggest is the RT-AC68u. I found one on sale here for 141$. If that is too much I have other suggestions but that should get you started.