Ski boat as you say, or ski/wakeboard, or strictly wakeboard?
Lots of things come into play when selecting a boat. What are your wants, needs...etc?
Are you familiar with the I/O drives, Inboards or V-drives?
Do you want ballast? If so how much, 500, 750, 1000lbs?
Do you want a tower & pylon, tower only, pylon only?
Quality begins with the hull. Fully fiberglassed monoque designs are the best, but more costly as well. Foam stringers reduce the overall weight of the boat (most newer boats are foam anyway, older are wood). All cleats & hardware should be through-bolted with an aluminum (or other metal) backing plate. All hardware should be stainless steel.
Interior should layout to your needs. Sun deck or passanger space - ergonomics. Interior should have atleast 30+/- oz. vinyl. Removable carpet is a plus for hosing out after a trip.
Dual batteries. Good stereo. Lights. Good trailer....the list goes on