For under 100 units, there are several firms who can do a good job. In Columbus, that size can comfortably be managed remotely (from a central office) with no on-site staff. Be sure to talk to Panzera and Solutions 4 Real Estate. Maybe one other... ;)
Over 100 units, it's a totally different ball game. Different pricing, different companies, on-site management. I suggest talking to Link Real Estate Group and Oakwood Management.
I would also draw a pretty clear distinction between C class and B class. Not many firms can do a good job managing C class properties of any size, especially C- (which is what many people call C). Again, different set of operators and management companies. For example, we take on B class and some C+, but never below that. I know Panzera and S4RE are similar. If you are looking at management for true C class or below with under 100 units, talk to Donny Thompson with ERA. Over 100 units, no idea.
If you PM me I can give you contact info for all these companies.