I haven't had a chance to check out the Makita model, but I've used both of Milwaukee's main offerings. I like the M12 better than their 18 volt, seems more controllable, but the 18 volt has better balance as the battery offsets the tube of caulk somewhat.
One thing I've noticed with the battery powered caulking guns is that they're great when you're running beads as they'll dispense a constant flow at whatever rate you set. Not as good when you're placing lots of spots, there's no "resting" spot on the trigger, where the ram stays pretensioned but not dispensing and when you do release the trigger the automatic drawback pulls the ram back far enough so you won't have any sort of drip, but it takes about 2-3 seconds when you press the trigger before it starts dispensing again.
My personal preference is for a pneumatic caulking gun. Been using a basic campbell hausfeld for years now. Instant let off as soon as you release the trigger, variable speed based on trigger pull as well as being able to regulate it by psi, and because of that variability, you find the resting spot for the trigger where it's pressurized and ready to dispense with just a fraction more pressure on the trigger. I love the CH pneumatic for putting up InsoFast insulation panels, two guys and we can get em placed almost as fast as we can unpack them.
