Interesting thread; thanks for starting it!
I live in Edwardsville and presently invest in both Glen Carbon and Edwardsville. I'm trying to get educated about the Missouri side. So far there are pros and cons and it's a trade-off. Here's my thinking:
I know this (IL) area a lot better so it would be easier to accidentally invest in a declining area in St, Louis/STL County. That said, as noted above taxes are lower in MO. But that could be offset by higher insurance in a higher crime area, Edwardsville/Glen Carbon doesn't have any declining areas that I'm aware of.
Between the two cities I prefer Edwardsville. Glen Carbon has a yearly inspection requirement (not a bad idea on its own) but the pass/fail decision is purely subjective and depends on the mood of the inspector. I've been bitten by some pretty bogus violations. To be fair other inspectors have pointed out potential issues and saved me headaches so maybe the glass is half full. But between the two cities I prefer Edwardsville and Glen Carbon would have to be a pretty good deal for me to buy.
Lastly I'm starting to look at Bethalto but can't say anything intelligent about that market yet. Good luck and thanks again for starting this thread!