Modern Vespa

I've searched and searched, but couldn't come up with a definitive answer. My rear Sava has reached the end of it's life, so it's time to replace. Which tire tends to get longer life, between the Pirellis, Michilin Pilot Sport and City and Conti Zippy 1. Was it the Pirellis that seem to last longer than the other two brands? I'm looking to find the best miles per dollar, not neccessarily the cheapest tire.

One other thing... is really that bad to mix brands/type of tires (of the correct size)? While my rear tire is spent, my front still has plenty of life left. I just don't want another Sava on the rear.

Hello Mongoose
With my first Sava,I've made less than 6000km, with my Michelin PILOT CITY, I've made more than 8000km.
No problem to mix with the front Sava who have now 15000km (time to change!)