Here's my take on grease and grease guns.....
I'll preface with I was a heavy duty diesel technician for years and after having kids I changed jobs as an amusement ride mechanic.
I've used just about ever automatic grease system, electric, air powered and hand powered grease gun out there. I prefer a hand operated gun. Amite is my preferred brand, but a Lincoln would be second choice.
At work with the number of rides I take care of and the high level of greasing we do, electric and air powered has won over. Just too much to grease and too little time to get it all done by hand. (All excess grease is cleaned up, zerks are wiped before and after every greasing. Can't have grease getting on a patron or on the pretty paint jobs.)
Grease. As stated there are different greases for different tasks. Use one that meets the mfg specs and life will be good. I will say molley grease isn't the only grease out there that contains a solid lubricant. It is about the cheapest effective make up for high load, high friction areas. I never use a calcium/ aluminum based grease on anything. Lithium and molley versions have always been my go too, I have been favoring a few synthetic greases recently, but just because I have been using them pretty frequently at work for the past few years.