I like two barreling here, we've got strong outs and he should have a tough time calling two streets on that board - keeping the pressure on him here makes a lot of sense to me.
ch/r is interesting - 6x, 2x, A high, and miscellaneous pp's are going to have a very tough time calling. A drooler like this I think will sometimes call a ch/r w Tx, JJ, and always w Qx, 2 pr, and sets. There's a good chunk of dead money in the pot - it doesn't need to work that often to show a profit. His bet size being so small is also allowing him to fold to save half his stack (if he'd bet closer to pot, he shouldn't be folding).
ch/c I think is the worst of the three options - a guy this passive (25 is AFq?) is betting for value with something, he's not bluffing
a busted fd i don't think (though I wouldn't be surprised by 6x or something equally weird), I think he checks back. The bet size is so small that he doesn't need to be bluffing very often to make a profit here, I just don't think he's bluffing often enough (unless he thinks you're a spewtard?).