Well, I can't speak for the other programs (I didn't interview at any of them), but I'm a resident at Iowa. So I guess that makes me both an expert and completely biased at the same time (as we've seen from the flood of postings after any program gets maligned on these boards).
(1) Malignant? Nope. Not at all. This is the Midwest. That's not how we do things.
(2) Teaching quality? I'm not as sure on this one, as I'm just an intern yet. My sense is that it is good. The main daily ones are stroke rounds each morning and varying noon conferences, but there are also subspecialty ones at other times if you have an interest. Some residents on inpatient services keep busy enough that it can be tricky to fit in both.
(3) Are the residents happy? Yep. Does everyone get along with everyone in a glowing celestial hugfest? Of course not. There is periodic interpersonal drama here and there. And since call is frontloaded, 2nd year residents have it the toughest (good thing the intern year isn't too bad). But as a whole, the quality of life here is pretty good: nice people + nice hospital setting + easy town to live in = happy residents. And hey, the program (and thus, the call pool) just increased to 6 residents/year, so even the 2nd year is getting easier.
(4) Research ops? I'm not a huge research person, so I'm not the best person to ask. My understanding is that Iowa has a large basic neuroscience contingent, and there are plenty of opportunities for those that want them. I think there's a lot of behavioral stuff especially, since most of the people who worked with Damasio stayed here when he left. But I think there are solid opportunities in other fields, too. I'm not sure about 6-month research electives or other options - I haven't been interested in doing that, so I don't know about the possibilities. The more research-y residents haven't seemed to have any problems, as far as I know.
So yeah, I'm pretty happy here (and that's even after coming here from the oft-touted California). Definitely worth a visit to see if it fits you.