Sony and Panasonic make all the miniDV tape stock. The other brands buy this stuff and stick their name on it. The big questions are....
1) What is better, sony or Panasonic? Most people are happy with what they use, so it probably a moot point.
2) Can you mix brands? There is some discussion about mixing sony and Pan. tape. It has to do with the mythical wet vs dry lubes used on the tapes. Mixing them can supposedly create a goo that clogs the heads. Is this true? Some say yes, others no. I use Sony, don't need to change and don't want to just in case they are right about it being bad.
3) If mixing brands is bad what are you buying if you get TDK, Fuji, etc? They can switch between suppliers so what may be Sony stock can later be Panasonic. Brings us back to question 2...will we ever get a straight answer?