Ever ridden in or driven a rig with a spooled front end? I guess not or you wouldn't be asking. I'm now running ARBs front and rear. When on the trail, I leave the rear locked almost all the time whereas the front is locked up only very rarely. There just aren't that many sections where the front locker is necessary (as opposed to just helpful). However, when the frontend is locked (and a locked up ARB is the same as a spool or a welded diff - absolutely no differentiation) it is MUCH more difficult to complete normal trail maneuvers. You can feel the front end fighting to avoid any straying from a straight line - which equals significant added stress on all the front end components. That means not just the gears. carrier, axles, u-joints and hubs, but also the housing and all your steering components as well.
I love my ARBs because of the flexibility - on or off at the flick of a switch. But I would go for an automatic locker (such as a Detroit or a lunchbox locker like the Powertrax) in a heartbeat over either a spool or a welded front end. It just causes you to lose too much flexibility.
An auto locker does not drive both axles at the same speed any time power is applied, contrary to popular belief. Rather, it prevents either axle from turning slower than the ring gear, but will permit either axle to turn faster than the ring gear. What this means is that if a rig is turning under power on a surface with good traction, the inside wheel will be driven at ring gear speed while the outside tire will be driven - by the friction of the ground - at a speed greater than ring gear speed as it traverses the longer line around the outside of the turn. But what does this really mean? It means that any time your rig turns even slightly on any surface, simple geometry requires that either the outside wheel turn faster to cover the greater distance, the inside wheel turn slower to cover the shorter distance, or one or both of those tires must lose traction for the vehicle to turn. No exceptions. An open diff defaults to letting the inside tire turn slower (or to sit still while the other tire spins). An auto locker defaults to allowing the outside tire to turn faster than the ring gear anytime there is enough traction to turn the tire rather than drag one across the surface. A spool or welded diff defaults to forcing one or both tires to lose traction and either be dragged across the surface (outside tire) or made to spin faster than it is moving along the ground (inside tire). Recall that this is for EVERY time you turn the steering wheel, varying proportionately with the extent to which the wheel is turned.
Sorry for the long expanation. To put it simply - unless you only wheel in straight lines or don't mind spending your time and money replacing worn or broken parts - save up for an auto locker for your front axle or save up twice as long for a selectable locker.
Good luck.