Spool beats 'auto' locker for handling, hands down. Harder to park, but thats the only down side, and a 40/60 rig it shouldn't be an issue at all. FAR easier (and more even, too!) on tires than an open diff with a heavy foot. They don't break, either. I've broken 3 detroit lockers, never tried a lunch box locker, but its gonna be weaker still.
My explorer has TrueTracs front and rear. Realistically, its 85%+ street, 10% dirt/gravel, and 5% offroad/sand dunes. Torsen type LS is the ONLY LS worth using, period. clutch ones are locked until the going gets tough, then they bail out on you, if they didn't wear out 20000 miles ago... braking with them helps a very little, but with a Torsen (truetrac) it makes it LOCK.
If you actually wheel your rig (on purpose) and don't mind the quirks on the pavement, its pretty tough to beat a spool/selectable rear and locker/selectable front. Elec-Trac's front and rear....mmmm too bad not available when I got my 8.8 Truetrac.