For anything driven on the street, I wouldn't recommend a spool on either end. I'm a big fan of being able to turn my rig.
I'd go for a ratcheting locker (Powertrax No-slip, Detroit Tru-Trac, or the like) on the back end and a simple posi up front. The best way to go would be a automatic locker in the back and a command-actuated locker (ARB or one of the electronic lockers) up front. That would be the best of both worlds for your situation -- the ability to turn the rig on command, yet still have all four wheels spin when in the mud.