Whatever you get, you want something with low moisture content. I typically shoot for 15% or lower. It will transfer more heat to your oven and weigh less when transporting to your cooking site.
I like oak because it's plentiful in my area and makes a longer lasting coal bed. If you go on Craigslist you're going to find a wide range of prices and an even wider range of what people's idea of 'seasoning' is. There are some real shiesters out there (saying it's dry wood, or a certain quantity when it's not) and unfortunately it ends up being a trial and error type thing. If you've got any WFO restaurant friends I'd get a rec from them.
Wet wood, species, price, and verifying the quantity of wood you're getting are all things that will directly or indirectly cut into your bottom line.