I've rented from Jans, Christys, and Cole Sports, always demos. No complaints about the equipment at any of them. I think Christy's was the most expensive, but if I recall correctly, not by a whole lot (be on the lookout for coupons, and I think one or two of them give you a break if you reserve in advance).
Since we were staying in Park City and doing most of our skiing there, I never really looked at anyplace out of town, figuring it would be a real PITA driving back to Salt Lake City to fix any kind of problem.
It's also fun trying different skis. If there was any advantage to one over the other, it was that Cole Sports had locations at PCMR and Deer Valley (as well as in town) so if you're skiing those places, it's real easy to switch midday.
Although certainly not the cheapest way to go, demos are your best (sometimes only) chance of getting good equipment.