firstlt, bring a magnet with you, or check to see how much of your grill is made from 304 (300 series) stainless steel, which is non-magnetic and more rust proof. lots of grill only have a 304 lid, but the rest of the grill is 400 series, the magnetic type, sucseptible to rust.
some people go as far as to make sure even the rivets and screws are 304, but then you're talking big bucks. if you intend to buy one that'll last 25 years or more of heavy use, then it's worth it.
anothet consideration is the guts. because of the heat, the guts are going to wear out. brass burners (aka venturi tubes) will last longer, but again $$$.
fortunately, venturi tubes are easy to replace, so you really don't need brass ones (unlike the chief who brags about his at every chance...).
also, depending on your clime and arachnid population, you may want to get a grill that has easily removeable venturi tubes. certain spiders love to build webs inside the tube, so if you see thwt your flame is yellow, not blue, and not reaching the end of the holes, yoy've got a web. pulling the tubes and jamming a thin stick ir branch to break it up is the easy fix. heat will finish it off.
finally, as far as features goes, get one with a searing burner and an a.c. powered rotisserie and rotisserie burner.
the searing burner is great for charring peppers, cooking high temp foods such as shrimp, calamari, and delicate veggies like asparagus and mushrooms.
battery powered rotisseries are a pita to have to deal with the batteries, and often don't have enough torque to rotate heavier and asymmetrical cuts of meat evenly.
one more thing: unless you intend to roll your grill in and out of a garage every time you use it (in which case you'll need to check the gas connections in and out of the regulator and the flow through the venturies), invest in a good cover.
oh yeah, don't put the grill where the smoke can blow directly on the siding of a building or on a short deck. the heat can be dangerous if close enougj, and the smoke carries grease that will stain the siding that's really tough to remove.
hth.
pm me if you'd like more info or help.