Hi,
I mostly use Midway, Graf's and Ballistic Products myself. A buddy has Midsouth on his list, and Natchez comes up in the conversation every so often.
One thing I've learned over the years is to watch your TOTAL cost carefully. For example, Midway might beat Graf's a bit on an item's price, then charge enough for shipping to offset Graf's fixed rate shipping cost. Maybe a couple of vendors will even out otherwise, but the order includes powder and/or primers, and someone's having a "half price haz-mat special" and so forth.
Ya gotta watch carefully.
Then check the "In stock" status, too. I don't like placing backorders, but my brother in law does it every so often. He says Cabela's is his choice for "out of stock" items as they're a bit more expensive than some others, but offset that by handling his backorders better than some others have.
So that adds another thing to watch... all in all, I don't think I know anyone who's a "single source" buyer!
And, once you've ordered from them, most of the vendors will put you on their "specials" list. A lot of good prices can be had if you have Rainman's "shopper's eye" and keep it open for their flyers and e-mails.
Rick C