If you're paying for 200Mbps download speed and don't foresee yourself ever purchasing a higher-than-200 Internet package, then I'd suggest a modem whose max download is not over 200Mbps.
The 200Mbps speed comes through the cable, to the modem, to your router (if you have one) and then gets passed on to your devices. Through your router, you can dictate what device gets what speed, who gets precedence, etc.
TLDR: If you see a number of channels listed on a modem, this can give you an idea of how fast the modem is; most have four or eight "down" channels and four "up" channels. DOCSIS 3.0 allows up to 43 Mbps down, so a four-channel will give you 172 Mbps download speed, and eight will give you 344 Mbps. 16-channel routers are starting to show up with a claimed maximum download speed of 688 Mbps, which is blazing fast.