I've got an AD with one of each. The only pro I can think of is a little easier drivability with the 4 speed. 2nd gear is synchroed on the 4 speed so downshifting is easier in traffic. You very rarely use first. With the 3 speed, in order to downshift to first you've either got to come to a complete stop or double clutch as you know.

Cons, that 4 speed weighs a ton. I can bench press that 3 speed in place, but the 4 speed is a bear even with a floorjack.

If it was me, I'd leave the 3 speed if you're planning on keeping it stock.

Bob