Internet modem/router

We are new Cox subscribers and are having the Cox installation in two weeks. The package comes with a cable modem and router, not sure if these are one or two separate items, for which they want to charge $10 a month. I wish to buy my own modem/router, and wish to know which is a recommended way to go-separate modem and router or a combined unit, and which ones are recommended for the 16x 4 channel internet? Regards, Russ LaRose