Ball diffs are good because you can set them when you want.
But definetly the oil gear diffs are better in performance. The only minus is that they are heavy but.... now that plastic gears are much stronger someone like Xray (with the 2012 spec of it's T3 electric chassis) is coming up with gear diffs

Yeah when you have to rebuilt them it's a dirty affair but you do this few time in a year.