They are both standards for cable modems. It allows head-end equipment makers to be compatible with a variety of end-user equipment.
I don't know the details of 1.0 vs 1.1. I'd expect 1.1 to be backward compatible to some degree, but given the choice, I'd probably want the 1.1 for whatever updates / corrections / improvements it may offer.
Check Google.
FWIW
Scott