I'm currently using Masters and Blue Diamond. Masters has the best bang for the buck but I believe Blue Diamond to be far superior.
Masters chalk is messy and I can see a cloud of blue dust as I chalk with Masters, not a problem with Blue Diamond. I think Blue Diamond stays on the tip longer.
I also have found that Blue Diamond is very similar to a cube of pre flag Masters that I have.
for $4 a cube it really isn't expensive, Masters is just really cheap. I bought 2 cubes of BD about 6 weeks ago, one cube is just getting past the wrapper and the other cube was stolen off a table about 20 minutes after playing.
I've been known to do this but it wasn't me this time.