Paycheck.
Ask yourself how you really plan to use the truck.
If you plan to stay on roads, the LS diff is much better behaved and will provide adequate traction for most conditions. If you occasionally venture off road where the terrain is not difficult, the LS diff is still the best option.
If you plan to spend considerable time off road in difficult terrain, the locker will provide power to both wheels under extreme conditions where a LS diff is marginal at best. When a locker is working, both wheels will turn, even if one has zero traction or is in the air (a LSD must have SOME traction on BOTH wheels for it to work).
NOTE: All mechanical lockers will bang, chirp, click, and pop on pavement. Occasionally, you will get a bang that sounds and feels like an axle shaft or u-joint broke. Any difference in rear tire pressure will cause torque steer with a locker. Driving on ice can be treacherous with a locker because when it locks, the truck will usually try to swap ends without warning. This is considered normal!
A third alternative is the air locker. It runs as an open diff until needed, and then sends power to both wheels when it is locked. The chief disadvantage of the air locker is cost.
Someone who really knows what he or she is doing should install any alternative diff. Proper setup is almost black magic, and requires a "feel" for backlash, preload, and gear engagement pattern. It can't be close - it has to be exact. If your dealership has a tech that moonlights for race teams, let him do it. Otherwise ask around; find the person in your area who changes gears for racers.
FWIW: I have a lockright in the rear and an air locker in the front of my 94 (the Detroit was not available until recently). My 85 F250 and Sue's 01 ETH both have LS diff's. The locker will always win the traction war, but the LS is much more friendly on pavement.
Dave
------------------
1994 2500HD 4X4 modified for off-road camping
2001 2500 ETH/DEE QC SB 4X4
Fritz's Dodge Ram Tech Page