50% MLS
25% My own marketing
25% Wholesalers
On the MLS I'd say about 10 offers for every one accepted. If it's the listing agent calling my buying agent then it's more like 80% acceptance.
I look at every property I put an offer on. There are a lot of wholesalers/rehabbers that take the shotgun approach and throw offers on everything until they get one. Inevitably they back out on a fair amount and the listing agent gets pissed. Then the listing agent gets ticked off they stop looking at offers from those people and call my agent to have us submit a real offer. I've picked up quite a few deals after 2 or 3 offers fell apart because of incompetent rehabbers and wholesalers, and I got it for cheaper then they had a contract for.
I get more deals from the MLS because I have a reputation of closing on what I offer, I don't back out from inspection contingencies (I know what to look for and have yet to find any big surprises when my inspector comes in), and my cash (or financing) is always ready at closing. Short inspection deadline, large earnest money, and short closing deadlines are always in my contract.