First thing I would look for is a W- or WS- cleaning code. This means that you can water clean it. Urine, vomit, spit, and body oils all need to be water cleaned.

The second thing I'd look for is a tight weave to avoid snagging from claws and teeth. Add to this a high-rub rating.

A Wyzenbeek machine is used allowing sample of the test fabric to be pulled tight in a frame and held stationary. Individual test specimens cut from the warp and weft direction are then rubbed back and forth using an approved fabric as the abradant. The number of double rub cycles before two yarn breaks occur or noticeable wear is observed is recorded as the fabricÂs abrasion rating.

Martindale is an oscillating test. Fabric samples are mounted flat and rubbed in a figure eight like motion using a piece of worsted wool cloth as the abradant. The number of cycles that the fabric can endure before fabric shows objectionable change in appearance (yarn breaks, pilling, holes) is counted. Number of cycles determines abrasion rating.

After that, I think it's a matter of personal preference. I'd probably go with a quality microfiber or polyester.