John, As a long time(45yrs) Kodachrome user, I believe there is nothing to touch it. People rave about Velvia and I use it for the convenience of E6 processing, however, when I'm enjoying a slide show and my Kodachromes come up on the screen, it's like WOW! The sharpness, the resolution, the gradation, the neutrality of colours, the smoothness, it's everything. Even the smell when you get back the box of slides.(Jay Maisel used to comment on that) But given the difficulty in finding current stock of Kodachrome 25, I use Velvia...it is good stuff.
I even manage to keep a supply in the deep freeze of Kodachrome 64 in 120 size!
Kodachrome's shortcoming was not the film but the company behind it. Kodak couldn't give a s=*t about it's customers and I'm sorry to say that my freezer is full of green boxes, rather than yellow boxes as was the case 10 years ago.
Colin