Good questions and fair questions.
To answer them honestly though, it kind of matters what it is that you are trying to sell. Though there are several choices available, some sales might be better suited for some houses. As an example, REA's auction is a really big deal every year and it gets tons of attention. The catalog is huge and it is full of incredible stuff. If your items would be headliner type of material, that might be the best avenue for you. If, however, it was something more common like a high grade Goudey Ruth, it might get shuffled to the back and not get the attention that it would in a different house. I know that is the crux of your question, but in order to answer it effectively, the scarcity and desirability of the items is also very pertinent. REA is a once a year deal. Other auction houses have great items too though and have auctions more frequently.
Depending on how much you have, spreading them out may not be a bad idea.
To answer your question the best I can without knowing what you are going to be auctioning, I will say this... personally, I would consider:
- the suitability of the items to be auctioned (weighing "standing out" in the auction)
- the auction house's reputation,
- the amount of the buyer's premium (or vig)
- the willingness of the auction house to wave any seller's premium (should be 0% if you have really nice stuff),
- the visibility and advertising associated with the auction,
- how quickly you need your money, and
- where the auction house is located (since that could remove significant buyers due to state taxes),
Those items are the ones that I would consider. Good luck!
Brian