While any of the above mentioned platforms will work, I think the primary considerations for a 'truck gun' is ease of storage and access, appropriate power for the task intended, and reliability in less then ideal maintainence situations.
I would elect the mini-14 in a synthetic stock for this given the currently discussed rifles.
Some basic reasons for my choice:
- The Syn stock is not going to get all mucked up and chipped easily - but wood is also available for any purists out there.
- It is streamlined and compact, ie: you dont have a 30rd magazine, scope, 2 flashlights, laser pointer, gps, Flash Gordon decoder ring, and a cigarette lighter mounted on the rails that will snag up on things and make it hard to get out from behind the seat or off the gun rack
- It is reliable as hell, and shoots even if poorly maintained.
- It wont garner undo attention by anyone who sees it in your truck lying next to your "Live Free or Die" bandana
- It has acceptable firepower yet is easy to handle and keep on target by those lacking Popeye's forearms.
All fun aside, I think it is a great choice for an all around truck gun if you are looking for a SA platform.