If you carry large amounts of fluids (see:beer), having a CART with a cooler in it is optimal.
If you're shorter, maybe you should have gone with a Delta.
The thing I found as a positive (for me) for carts over bags is that they took the strain off my back and moved it to my legs. I had to get used to the extra work my legs were doing. Hope you figure out a way to ease the pain from your knees.
Pushing the cart whenever possible is much easier on your body. I've noticed that the cart takes the load off of your back and shoulders but does put the load on your legs. Pushing it rather than pulling does make a significant difference. I was on the fence with mine, same backpack Zuca, but it has won me over after a few weeks of use.
All the points I would make. I have a GoKart and it is probably the best "seat" of all the carts.....for me. It is wonderful on cart friendly courses and is a saving grace during the pace of tournament play.