I usually try to avoid hambugers when on vaction at WDW, but the past trip we got in late and had to get a double bacon cheese burger at Riverside foodcouts and it was pretty good I was surprised probably not the best burger but not bad. We have gotten burgers at Pacos Bills and liked them but usually go for something other then burgers.
The Grand Floridian Burger at GF Cafe has pieces of lobster on it and is something like $17 or $18. People should understand that. It is really good though!! Also agree Le Cellier's burger is very good. The Plaza has decent bacon cheese burgers, not great, but better than the CS burgers and a good lunch option when in MK.