What is best will depend on lots of personal situation. If you have lots of grease zerks, maybe an air powered but I've never been into the volume to make it worth getting out the air to do it.
Next stage might be battery but that doesn't fit for me as I've never had more than a dozen or less to do at a time.
I used a lever type that took the large cartridge for years but I got tired of trying to hold the hose on the fitting and needing two hands to pump so switched down as the number of zerks kept dropping.
I still have one of this type small mini gun that takes the mini tubes but I have to admit that it rarely gets used as having it done is so cheap on the oil part that I was barely breaking even when doing the oil and grease, so I have not greased a vehicle in several years!
I do still have one item that I grease but it is my wheelbarrow and it runs such short trips and such low speed that I'm not worried about overheating the bearings!
Unless you have other uses besides the RV, I might suggest one of these for ease of use as it takes a long time to empty even the small tube.
I like a flex hose and using one hand for the gun and one for the fitting? But does your RV still have fittings to grease?