I moved to Forest Park recently, and have been on a great-burger quest for the past few months. Hands down, the best so far is at Deko's at 7445 Madison in Forest Park, between DesPlaines and Circle Ave.
Goldyburger is good, but not amazing-good.
Byron's is ok for a fast-food style burger, but it's fairly bland and the patty is pretty generic.
Sub Tender has the great grilled onions, but it's rather greasy, even more so than a regular burger of its genre. The garlic-butter fries and subs are the best though.
I've heard good things about Shanahan's, but I personally had a terrible experience there with the burgers. It's served on thin white bread, not a bun, which was soaking wet when my burger arrived. I ordered medium, but the burger was literally cold and raw throughout when served. The waiter was apologetic, and comped us a slice of key lime pie for the trouble and incredibly long wait, but the 2nd burger he brought out wasn't much better.
But Deko's... Deko's is where it's at. It's a great little dive, and you'll always see the same two guys working the counter. The burger is fresh and juicy - definitely tastes like a real burger, not a fake-fast-food compressed patty. Shredded lettuce, mayo, tomato, onion and ketchup seem to be the standard condiments. I love the fries too, but I think they're just generic crinkle-cut fries from a bag - still always crispy and delicious though. I also recommend the gyros too - shaved fresh off the roasting spit, and not greasy like at other places I've tried.
I never see any mention of Deko's in the threads about Forest Park eats. Why not? How can a place in the middle of the Madison street bar strip be seemingly unnoticed, but so good? Has anyone else been here?