I'm in the camp that it doesn't matter most of the time. The cable modem is going to get whatever programming it needs from your ISP and that's going to set your cap. I don't think you're going to see download speeds in excess of 100Mbps any time soon, especially not on consumer cable services, so the 1Gbps ethernet port seems more like a justification to increase the price rather than a useful feature.
That said, my cable modem is a "Comcast Business Gateway" made by Motorola. It's what most of my customers use as well. The main thing I can say about that model is that they don't seem to crash very often compared to the consumer grade modems I've tried.