I pretty much use all Fuji, Provia 100F is the best general-purpose slide film on the market, period. While Velvia is the best "super saturated" film.
I still find uses for Kodachrome, but not many, especially now that KR25 is gone. I just isn't worth it...I honestly don't want to wait 2-4 weeks to get slides back. Especially when the results obtained by an E6 film like Provia (which I can get back in an hour) are far superior to KR64.
Maybe Kodak will get their butts in gear and develop a modern replacement for KR. But, from the looks of things, that will never happen.
To most people, the sky is the limit. To those who love aviation, the sky is home