routers

Both, the Cisco CMD31T is a 4x4 cable modem, not a router, good up to Preferred service.  The EA3500 is a router.  What do you have connected to the cable now?  Anything, another modem?  You need a modem connected to the cable and a router connected to the modem via Ethernet or you can use a gateway which contains both.

I say neither. As mentioned, Netgear is a modem and you can get a better router then that for that price. Something like the Archer C5 might be in your price point. Also see here for comparsion between different models.