This like many things, this is a matter of opinion and conjecture. Many of the best Mini racers I know do spend quite a bit of time to get their diffs "right". I don't believe any of them would run a "crunchy" diff. It's odd that some prefer a gear diff and others a ball diff.

My preference is for a ball diff, primarily cause it is so much easier to build "right" and gives me the diff action that fits my driving "style". I have never had a build come out "crunchy" although it is possible if improper techniques are used.

Some tips
1. Never reuse metal diff balls
2. Always sand out any grooves in the diff ring
3. Polish the diff rings
4. Use antiwar grease on the diff balls and thrust washer
5. Loctite and tighten diff screw all the way down
6. Build it exactly the way the instructions say to

Again, I am just offering this as a differing view from some others that were posted. I am also not inferring that mine is the only correct opinion.