As an Artilleryman, I am torn between the M110A2 and M109 series - particularly the A6 version. I agree that the M88, particularly the A2 or HERCULES version, is great recovery vehicle.
On the wheeled vehicle front, I would have to say the HMMWV series. The M151A2s were nice in their day, but outclassed by the current HMMWV series (of course, you can't sneek around with a HMMWV the way you could with any of the Jeeps!).