I like the glass jars because they can be put into the dishwasher if need be to clean them up after use. Also, you can see if there is any mold and how much syrup the girls are using. Can't with a paint can!
Brian and Iddee, I assume that you are not using an inner cover when putting four one-gallon jars on your hives? I built a special inner cover with a four-inch hole in each corner, covered with some #8 hardware cloth. Works like a charm if you need to throw a lot of feed to a new package or swarm.