Most people will tell you to avoid a modem/router combo and buy them separate.
The best/newest cable modem on the supported list is the sb6183. Motorola is well known for quality modems. The 6183 is a 16x4 modem (futureproof).
The 6141 is also good 8x4 modem.
If you want cheaper than get the 6121, a 4x4 modem.
The difference between the 4x4, 8x4, and 16x4 modems is the max supported speed. Your 30/5 package will be fine with any of the modems. People buy the 8x4 or 16x4 modems for futureproofing or if they have higher internet packages (100mbps+). I am not sure if you will be able to buy the sb6183 anywhere, it might be rent only. In that case get the 6141.
Then, buy a separate router of your choice.