What do most homebrewers use... ball or pin lock soda kegs? What would you recommend I purchase?
If you know other homebrewers that keg, you might want to use what they use. If you don't, then it doesn't matter much. Pin locks are usually much cheaper. All of the brand new kegs being sold are ball lock and eventually that may be all that is available. If you get threaded disconnects though, it isn't hard to swap them out.