My best passport - with regards to number of stamps and visas, is lost somewhere in Australia, but this old one is pretty cool, too.
I have always travelled with my Canadian passport. It's the most harmless since nobody knows anything about Canada. A good thing when you're arriving by a fishing trawler from Aserbajdan into Turkmenistan without a visa or you fancy popping into Dagestan unannounced. Etc. Etc. Etc.