what is your budget? If you're looking to buy new gun and don't want to spend over $200,DeVilbiss Finishline guns will do, make sure it doesn't have a plastic air cap retainer ring,anything with 1.3-1.6 flid tip/air cap should be fine for base/clear
If you're looking at used guns,make sure it sprays right,some of the Ebay guns might be trash, you could drop a brand new gun on the floor and it will never spray right,rebuilding won't help either,also keep in mind, rebuilding kits and parts for high-end guns sometimes cost alot of $$, I had to rebuild my Walcom GEO FX gun last year and it cost me over $125 just for parts,I think it was almost $600 when I bought it ,but I love the way it breaks down the materials