I REALLY like Graco spray equipment, on their hand-pieces the aluminium collar that retains the main air jet housing is offen a problem when it is used very heavily (I'm talking 12hr days) as the threads tend to cross. But the guns pull apart completely making them such an ease to clean (soak overnight in thinners).

Good adjustment of macro & micro, good availability of parts and great guns. Parts can be costly, to the point where you are better off buying a whole new gun when only a few critical components fail but by then you've probably come to the end of it's life anyway.

SO I guess you should look at a gun that is built well, has a good reputation and one that is easy to clean and easy to get replacement parts for. I suppose the availability of jet/nozzles is also relevant.