Hi Ryan, you will probably receive many answers to your question because there are various ways to get leads for wholesaling. I do not believe there is one list that embodies the most opportunity because there are so many opportunities available. You have the option of off market properties like preforeclosures, foreclosure, for sale by owners and driving for dollars. Or, options you've already mentioned - probate, tax deferred, vacant,etc. You can also work with an agent who can create a hot list for you; but you will want to be specific on the exact type of properties you are looking for. Perhaps the agents list will be as close as possible to capturing various type of sellers because it may capture REO, probate, distressed properties, short sales, vacants, etc.
I would suggest networking with your local real estate investment clubs and see what's the best leads in your area (meetup.com, reionline.com, creonline.com or facebook). Also, there's a book called Real Estate Riches by Dolf de Roos - Chapters 7 and 8 provides great strategies on how to find leads for properties.
Best of luck to you!