Disclaimer: Not being a Chicago native, I've eaten less Italian Beef's in my life than some of you in
one day. As such, I'm not really a good judge for the Best, or even Any, Italian Beef. But I could offer an outsider's opinion on one of the strongest contenders on this thread - Johnnie's on North.
Short version: Sandwich was meh, everything else was 11/10.
I was biking past the neighborhood, and Johnnie's shows up on my list of Chicago institutions to try. Reasonably hungry, I thought meat on bread sounded perfect. I ordered my "wet and hot," which sounded odd.

Looking every bit as glorious as I imagined, I bit into the sandwich expecting great things. Then... it was okay. The bread was a bit mushy, but not to the point of being unpleasant. The hot peppers was one-note, covering up the other flavors (coming from someone who puts chili/peppers on everything). The beef? Because the ingredients of the sandwich are so unevenly distributed (big lumps of meat at one end, peppers only on the outside edge of the 'wich), it was difficult to get a representative taste of how all 4 ingredients worked together (bread/gravy/beef/peppers). I didn't get much flavors from the beef - it seemed undersalted. The jus was a bit better (I was enduring my way through the meat parts so I can get to the dipped bread part, not unlike the relationship between pie fillings and pie crust). It was too lean for my taste - I felt like I was eating overcooked brisket, one of the easiest way to annoy someone brought up in Cantonese cuisine. Perhaps the pastramis and corned beef's of the world are more suited for me.
On the other hand, Johnnie's is my
ideal for what a restaurant should be:
-efficient kitchen flow (sandwich ready seconds after ordering)
-people behind the counter are committed to getting food to your belly and nothing else (they don't even have a tip jar!)
-standing counter with open kitchen view for those who just want to grab a quick meal
-large outside tables such that in a busy service, communal eating is encouraged
-simple menu, with clear specialization of 1 savory and 1 sweet item (the italian ice was not bad at all!)
-reflective of local culture/history/products
-not really a chain (1 other location)
-regulars coming from all walks of life
-reasonably priced