For the Wagoneers, it depends. In general, the 7-leaves per pack is more sought after than the other pack (which came with 5 leaves per pack). But even if you get the 5-leaves pack, they'll still work. But as for leaf springs in general, I think they flex plenty for most off-road use so go with what you can get. Plus going with leaves means less work since you wont have to weld on some coils spring seats/brackets onto the axle -- assuming the chassis width is close enough (so you wont have to move the spring perches in/out)
Dont focus too much on flex because traction (locker, tires, etc..) and torque (gearing, etc..) are just as important, or if not more important -- you can't get anywhere w/o traction or the right amount of torque (otherwise you'll burn out the transmission revving too high and the vehicle becomes uncontrollable because it has to be constantly "bumped" over obstacles as opposed to just crawling over them).
