Two important components to percieved modem performance are connection speed, and host CPU loading.
I would say the most important is the connection speed, USRobotics are known to be good at this.
Next is CPU loading. As I understand it all external modems by default must be "hardware" modems. Internal modems may be "hardware" or "software", it depends on the model. Whatever you get you want it to be a "hardware" modem. The difference is in which component is handling compression and error correction, the modem or the host CPU. "Hardware" modems handle the compression and error protection in internal hardware and so the host CPU never has to worry about these tasks thus freeing it's time for potentially working on other tasks. "Software" modems require the host CPU to compute the compression and error correction tasks, and thus take up more of it's time resulting in a slower system.
In summary you want a modem with the highest connection speeds that minimally loads the host CPU. I think, but you should verify it, that all of the modems you mention meet these criteria. Besides that you just need to decide which features you like.