I like the one that works without removing a wheel.
I would venture to say the chain drive could apply more power under load then the friction drive.
I am going to say that open gear case is going to be tough to keep
Chain drive may be more efficient, but the farms of the day were powered by belts.
I'd go with the outfit Steve posted. Simple, easy to rig. Now, if I just hadn't been so short-sighted as to get rid of all the old flat-belt machinery over the past 40 years . . . when the Case Model D died, I didn't have any way to drive a flat-belt. Rats !!