I have 2 diesels with auto trannys and don't like either transmission. May do a 5/6spd swap when the auto behind my Cummins shucks out. Just depends on what you prefer. If you will use it mostly as a daily driver or in town, you will probably want an auto. If you plan on pulling alot of weight, you may want to go with a man. transmission. If you do get an auto, and pull with it, make sure you put a gauge on it so you won't get it to hot.
Thumbs up with the 12v. No problems in my 1 1/4 yrs. of ownership of my Dodge.
Good luck in your serch.