I think each model is specific to cable providers, per region. Cox is using SA where I live, but 60 miles away they're using Motorola DVRs.
Everything I've read would leads me to believe not to expect any SA box is better than another, just technically different.; like number/type of tuners, drive capacity, or HD output capability, etc. The loaded up interface, SARA or Navigator, tends to be specific to a providers.
I suggest you call your local providers' tech support and ask what they are using now, Sales might not be able to answer your question.