One thing I can guarantee is St. Louis has the single worst pizza in the world. They serve with some cheese abomination called provel. Absolutely brutal.
Anyhow, I avoid all pan pizza in Chicago that have becomes chains like Uno, Due, Giordano's, Malnatti's. Too many tourists and quality control goes way down. I like Pizano's (great grandson of original Uno chef I think), Ranalli's or Pequod's depending on what side of town I'm on.
Growing up we got thick pizza (different than pan) from Salerno's in Berwyn. Awesomeness though I haven't been there in 15 years.
My regular thin is D'Agostino's but some of my thin favorites are Nick and Vito's and Barraco's on the southside. Pat's and Castel Gandolfo are great. Like Danny Shennanigan I like Aurielio's too.
Chicago thin is different than NY thin (which is great) because it's squares instead of slices and it's more cracker like, sweeter sauce, thicker sausage chunks and crispier crust.
I can't say I've experienced much pizza outside of the US since I was more interested in other cuisines.