Assuming you want performance (traction) and not just long lasting, then generally you get what you pay for, and you also should match the tyre terrain rating to what you will ride on, or else get a tyre which is designed to be an all rounder. The China tyres are usually sub standard compared to the Jap and Euro brands. Tread pattern and size are important, but there is much more to a tyre, such as carcass construction and rubber compounds. The better tyres also have harder rubber around the middle nobs.
Bridgestone M404+M403 are unreal for traction on a wide range of medium terrain, and they hold up pretty good if you stay away from rocks. But you can only get the older design M402+M401 in mini sizes. So I did not buy them.
I expect that Michelin Starcross would be great (as mentioned by DURT) if you matched the tyre type for your terrain (eg. MH for medium/hard). But the places I buy at could not get them for what ever reason(s).
I've tried a Kenda Millville on my 14" front, and I was not terribly impressed. I tried a Kenda Carlsbad 19" on the rear of my 450 and it was ok on hard pack, really tough too, but did not hook up well at all in medium or soft loam. The Carlsbads are heavy too (in the larger sizes at least). Heavy tires can make you mini bike handle a lot worse because ordinary suspension will become crap suspension.
At present on my mini I have a pair of Pirelli MX Scorpion eXTra tyres, and they are pretty good for traction on everything, and they hold up quite well too. Loose rocks and blue metal stones hurt them the most. The best things about these tyres for me is: 1) When they slide in loose/hard surfaces the feel is progressive and confident. 2) With normal mini air pressures (like 13 to 16) my rims don't get hammered too bad. 3) They are pretty light weight too. So really happy. About $50+$60 for the set.
