Id put it in the rear, it will handle the stress of the locker best.

 

Hmmm... this depends on quite a few variables.
I have 2 lockers, sometimes I'd use the rear, at other times I prefer to lock the front.
However, either is relatively rare, as I lock only as a last resort.

In a specific spot where the Jeep is stuck - or just about to - sometimes the front has something that gives better traction under it, sometimes it's the rear.

On a decline, the front gets more weight and traction, on an incline the rear grabs more.
Locking is usually needed more on inclines than declines, so it's usually the rear that would benefit by locking.

Also, weight is not always what we want. There are situations when less weight is better - for 'floating' on some snow types, or deep soft sand for instance.

An advantage of locking the front is that you lock the wheel that pulls to where it's pointing.
When the rear is locked and the front doesn't point straight ahead, the rear pushes the front wheels partly 'against their sides', causing resistance.

Bottom line - If I can have one locker, I'd want it at the rear.
In practice, there were more occasions when a locked rear helped me than a locked front.