My favorite St. Louis-style pizza place is probably Uncle Leo's, but it's a hole-in-the-wall place in a strip mall in south St. Louis, like 20 minutes from downtown. The closest to downtown is probably either Failoni's, or Guido's on The Hill.
I've never been to the Imo's downtown; the location across from Forest Park at the corner of Hampton and Oakland is pretty good. All of the mom & pop places (Serra's, Pirrone's, Farotto's, Nick & Elena's, etc.) are farther out in St. Louis County.
Since you mentioned Detroit style, there's
Nicky Slice's Pizza Club, which started as a take & bake that's so successful they're in the process of opening a physical store on the Hill, so if it's open when you come to town, you might want to give that a try.