Buying modem to replace Comcast modem

I am planning on buying a modem to replace the one Comcast provided to reduce my bill. This will be for my average-sized home. I do not have much experience with modems and only know what a few sites have glossed over. From what I have gathered, the Motorola - SURFboard DOCSIS 3.0 High-Speed Cable Modem Model SB6141 and Motorola - SURFboard DOCSIS 3.0 High-Speed Cable Modem Model SB6121 are good. If they are I would like to know which one is better for the money as one is $92 and the other is $70. Thank you for your help. If any information is needed please ask.

I have provided links to the modems on Best Buy here: 

Not much difference between the 2, I'd go for the cheaper one. Good idea to switch to your own modem though, saves you a monthly fee and also stops them from using the modem they gave you for free wireless for your neighbors.

Any modem really will work.

Thank you for the help!

The main difference between the the SB612x and SB614x modems are the max number of bonded downstream channels, 4 on the SB612x and 8 on the SB614x. This isn't going to be a factor unless comcast suddenly starts offering 200+mbps service though, so you might as well save a few bucks and go with a SB612x.