As others noted, that information is in the MLS, but not (as far as I'm aware) available elsewhere.
If you were living in the same area as the home you want to sell, I'd suggest driving around that community and nearby communities to see who the most active listing agents are. That's not an absolute guarantee that they're the most successful at actually pricing the homes to sell, but it's a real good start.
The individual agent is more important than the company he/she is affiliated with. Both are important but given a choice between a top listing agent with a smaller company and an average agent with the dominant company, I'd choose the top agent.
You say the folks who have contacted you have been in the "low ball, we will take it off your hands, sight unseen." Those aren't agents. Those are real estate investors. There's nothing wrong with what they do, and many owners are willing to sell for a lower price in order to sell quickly and without having to fix the place up. Other owners, however, want what you call "a fair price." And that's fine, too.
Hope all that helps.