The Masters is not an Open. You can't get in without an invitation from Augusta. A few amatuers are invited, but very few.
I like both the Open Championship and the US Open. It's hard for me to pick one over the other, but I think if you put a gun to my head I'd have to pick the US Open. There is a part of me that enjoys watching the best in the world struggle with the game the same way I do.
Personally, I would like to see the 4th major (the PGA) moved. I'd like it pulled out of the US and turned into a version of the Masters, played every year at the same time on the same course. Call it the Old Course Masters, and play it at St. Andrews. Everybody (or at least I do) always looks forward to the Open Championship a little more when it's at the Home of Golf, and I think that the it would be great for that course to be showcased every year.