I bought a modem once - it was a DOCSIS 2.0 modem. A year later, rogers changed to the DOCSIS 3.0 modems, and I was renting again. I think at the rate that speed is increasing these days, it might not be too prudent to consider buying a modem at all. First, and obviously with the QA, and secondly, if rogers decides to change its network configuration again, you might find yourself renting sooner than you would like to; albeit with a very nice $200 paper weight when it happens ;).
L.