That depends on what streets you mostly drive on. Most will recommend the selectable like ARB. I have the Detroit in mine but I do not drive on snow covered roads. If you are in snow quite a bit I would go the selectable route.
I run a Detroit in the rear of my Dana 35, and a lockrite in the front of my 30. It is noticable on the street, just takes getting used to. Mine also is not a DD. Like stated earlier, most will suggest selectable.
The reason for the selectable front is that if you are trying to turn while the front is in a bind or has pressure it will want to go straight verses actually turning. Once the front locks up it can be a pain to turn. So a locked rear and a selectable front is prefered to some other setups.
Remember "It Aint Perdy Till It's Dirty"