Air operated are prone to leaks and you won't know you have a leak until it won't work.
Cable operated are very reliable but you have to run that cable just right for it to work and it could get snagged.
Electric operated are vey dependable, wires are easy to run in a protected way. This would be my choice.
Generally, the limited slip device goes in the rear first since that is where most of the weight is located. If you have a device in the rear, than the front makes sense. However, before I spent the money on a locker I would invest in a good winch for the front and then learn how to use it by praticing and taking a class if need be. Not only would the winch help you out more than a locker, but it will also benefit any others you run across.