- Buy one that is compatible with your ISP. That's especially important if you use it not only for internet, but also for a digital phone (VoIP).
- How do you define performance for a modem? It should handle the speed in Mbps that you get from your ISP and that's it. It can't go faster than that.
- For the lifespan, read http://www.dslreports.com/forum/r29329201-Equip-What-is-the-Lifespan-of-a-Cable-Modem, for example.
I'm tired of renting a modem and need to buy one that will last and provide reasonable performance with a long life.