Depending on how much I'm spending, warranty conditions and customer support become more important. Random China stuff and Amazon products I treat as a perishable because oftentimes getting faulty products replaced or serviced is not worth the time or effort, nevermind the inconvenience when part way through a grow.
As for light fixture qualities, output and coverage are my top two. I want enough grunt to get the job done but I don't want it all focused in the middle of the tent. For a 4x4 tent, I would look for independent video reviews which include real-time PAR mapping. I find bar-style lights do the best job at providing even coverage.
A lot of people find efficiency important (running costs), but depending on how important that is to you, it may not be worth paying top dollar up front for high-efficiency fixtures if its going to take 5 years to recoup that cost in electricity savings. It's a big selling point, and therefore more costly, so it may be worth quantifying how much more expensive high-efficiency fixtures will actually benefit you.
Considerations might include spectrum and tunability, controller compatibility, build and durability etc...
IME you will for the most part get what you pay for if you stick to established well-reputed brands.