I think the OAC and NCAC are definitely better than the MIAA, but Adrian can hang with anyone (and they have great facilities). My $0.02 on some schools:
Marietta (OAC): You have to start here because they're the Gold Standard for D3 baseball. The stadium, the national championship pennants flying high, the traditional NY Yankees style uniforms. It just oozes tradition. Seeing those pinstripes and interlocking "MC" still gets under my skin.
Wooster (NCAC): Coach P is an institution at Wooster and in the Mideast region. His numbers speak for themselves. They are without question the most consistently relevant program in the NCAC. They've had a couple great cracks at a national title, but haven't closed it yet. Had a couple rough seasons of late, but they were good last year and certainly will be again. Also adding turf to their field which is nice.
Adrian (MIAA): For us non-MIAA folks this is probably the extent of our MIAA knowledge other than tracking scores. Adrian regularly wins the MIAA and makes noise in the regional. They're a legit national program with great facilities. That field is top notch for D3, IMO. Know nothing about the school academically.
Heidelberg (OAC): They were awful when I played 10 yrs ago. But Palm had them competitive by my senior year and they've improved every year peaking with a World Series appearance a couple years ago. They came back down to Earth a little after that great senior class graduated, but they have talent and if they can keep it healthy they'll be very good again. They're the model for every middling program.
The great thing about the NCAC and OAC is that beyond the elite programs there are numerous quality programs. Programs that put it together not every year, but some years, and challenge for the conference. It's an absolute dog fight to even make the conference tournament. It really is fun. But IMO you can't go wrong with any schools like Denison, DePauw, OWU, Allegheny in the NCAC or BW, John Carroll, Mount Union, Otterbein in the OAC.