Well, I can't recommend a specific brand (I've relied on DSL over cable over the last few years, basically because it's cheaper) but I do know that every ISP in the world changes the model of the modem they use more or less annually for both cable and DSL. That means it's *really* easy to get stuck with a useless, expensive chunk of plastic and have to buy or rent a new one. I have a 200 dollar Cisco 678 in my closet that isn't even much use as a paperweight.
Bottom line: I'd recommend just staying with your rental scheme. That way if (which is to say, WHEN) they change the model on you, you can just have them ship the new one out and rent that instead.