Well, since you actually asked for opinions :D
I'm going with topbars to hopefully avoid treatments. The bees build the wax they can handle, and this is supposed to lessen issues with pests that get into the wax when a lot of it is left unattended.
Regarding mites, I'm hoping my bees regress in size while building their own comb. I forget for the moment how, but that is supposed to mess up the mite cycle. Also, on foundationless, the bees tend to build more drone comb, which is where the mites tend to lay. It's a good place for me to scrape and look for the mites and a place for the bees to clean out infestations (not a single mite so far that I have seen).
I'm also avoiding any "chemical" treatments. I'm hoping that with a lot of diverse habitat, natural comb and a lot of wild, untreated plants to forage on, my bees will be strong enough to resist disease. I know this is very "pie in the sky," but for now they are thriving. If they develop diseases, then I will have to figure out what to do. My life experience has shown me that preventive treatment for diseases that have not even shown up yet leads to its own set of problems...
As for small hive beetles, I had read somewhere that they are in WI but not as big an issue since winter tends to knock them back a bit. Again, in topbar hives the bees only build what they need, so it leaves fewer places for the beetles to hide.
Actually, these methods could just as easily be applied to a Langstroth hive--just going foundationless. I guess I will need a couple years to let you know how they've worked for me, but they seem to have worked quite well for Michael Bush in Nebraska and I'm thinking his climate is not dramatically different from ours...