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I'd venture to say that KC and Charlotte, NC are the two best DG towns in the world.
STL has a ton of nice courses in and around the area.
I can help you out with a few suggestions. Of course, these are all personal preference...
If you like a course that is well established, challenging, and ALWAYS has groups of locals you can join up with - Jefferson Barracks DGC
If you like a course that has a bunch of elevation change, length, and nice scenery - Sioux Passage DGC
If you like a course that is technical, tight, and may cause you to lose a few hairs - Endicott DGC
If you like a course that hits a nice middle road in terms of challenge, has nice elevation, and ALWAYS has a bunch of locals present - Quail Ridge DGC
If you like a course that has a nice mix of all of the elements (elevation, length, etc.) and is right next to the best place in town for a beer and a bite to eat (Fast Eddie's) - Rock Springs DGC, Alton, IL
I could go on and on here. Let me see if I can come up with my Top 10 list of courses in and around the STL area (within an hour of downtown or so).
1. Sioux Passage Park - STL
2. Jefferson Barracks Park - STL
3. Foundation Park - Centralia, IL
4. West City Park - Festus, MO
5. Endicott Park - STL
6. Rock Springs Park - Alton, IL
7. Silver Lake Park - Highland, IL
8. Woodland Park - Collinsville, IL
9. Quail Ridge Park - Wentzville, MO
10. El Shaddia - Old Monroe, MO
Hope this helps!