Yup, what they said is all true. But, it kinda depends on what you are going to be using your truck for. If you are going to be hauling a lot of heavy loads, go with blocks. If you are just looking for the "look" and a good ride, I would go with springs. The capacity wont be quite as much I don't think, but you will def get a better ride.
go with the leafs, blocks will increase the leverage on your diff and axle wrap will increase ALOT. especially with 6 inch blocks. if the springs have a lighter load rating you can always add air bags.
1978 Ford Bronco
ZF-5 NP 205 10.25 rear Dana 60 front
Denny T fuel pin 366 governor spring
HX 35 turbo BD exhaust brake