We usually end up at Backlot Express, as it is tucked away and has a large seating area some indoors some tucked away in corners. It has a decent menu and it has serve yourself drinks. ABC Commissary can get crowded but is entirely inside with a large seating area, also they have an Asian salad there that I like. If eating outside doesn't bother you, then the Studio Catering Co. has really good sandwiches and a bar tucked around the corner for some nice adult beverages, also note it is a full bar that serves any drinks, not just what is on the marquee. Fairfax area, over by the Tower of Terror and entrance to Fantasmic, has several stands serving different items at each with a common seating area. I like the BBQ there and hot dogs at the stand at the end nearest the Tower of Terror.
I agree with the other posts as I also avoid Pizza Planet, we ate there once and once was enough, unless you like the Disney pre-made pizzas that is.
FUNNY STORY, or at least funny to me. I had probably been to Hollywood Studios 6 times, before I even noticed the Backlot Express quick service restaurant. It is that tucked away, since I found it I eat there almost every trip and there is always space to sit and never too much of a line.