Air greaser in the shop (Lincoln) on a 150 pound drum of grease but for the field, always a manual lever gun for me. I use the clear polycarbonate barrel on a Plews lever gun with a filler nipple on the top so I can fill it with my shop grease gun. Much prefer a manual gun, especially on double cardan (constant velocity) driveline joints where over greasing can destroy them. Standard Alemite coupler too, the one where you can adjust the jaw tension.
Never considered a cordless grease gun and I grease a helluva lot of zerks too. Like the other poster stated, you can buy a ton of grease for the cost of one. Not in the cards for me.