which modem is better?

I recently decided to upgrade my internet to Xfi complete. For $25/month, it includes unlimited data and a modem. When I initially signed up online, I wound up going to my local Xfinity office soon after to get a (white) modem since I wanted to start access of it right away. Hooked it up and all works great. They also wound up shipping me a black modem via UPS that arrived about 4 days later.

I need to return one of the modems (in order to avoid additional charges), but wondering which is better. The one I got through the mail via UPS appears to be model XB3. Its a slender black box. Has 4 ethernet inputs, 2 phone jacks and 2 USB ports along with a WPS button on the top.

The white one I got from my local office seems to be model XB7-CM. Its a little shorter and fatter than the previous one. It appears to have 4 ethernet and 2 phone jacks along with a button (assuming is for WPS service).

Are they both pretty much the same max speeds? I am currently at a 400Mbs plan so I'm sure both can handle this. The XB3 does have 2 USB ports. Can these possibly be used to hook up external storage devices? maybe not? I am not interested in the phone ports so no worries there.

I'm thinking the white XB7 modem is probably newer than the black XB3, but just wondering what the true differences are