I had a Lincoln 12V grease gun and liked it. It worked real well. Then Milwaukee came out with their 12V M12 grease gun, and since I already have a good assortment of their M12 lineup, I sold the Lincoln and got the Milwaukee. It works real well, too, but the Lincoln seemed to be a little quicker. Comparing the two by eye, the Milwaukee looks like it will take more abuse, has a rest to set it down on, and traps the end of the hose in a holder. On the other hand, the Lincoln was smaller and lighter, but I think I read the plastic pistol grip can break, and then you're pretty much done.
By the way, Milwaukee's M12 drill, drivers, impacts, etc. are great little tools. Surprisingly powerful for their small size, and good battery life. I highly recommend them.