I have a couple of dozen boxes of Kodachrome slides, and maybe half a dozen Ektachrome. I really liked Kodachrome at the time (when we were doing big holidays, Before Children!), but I must say when I came to scan the slides last year I very much preferred the Ektachrome! Very old slides that have been projected several times gather a LOT of dust, and you can't use the scanner's infrared dust-removal with Kodachrome (actually you can to an extent, by masking out the non-sky bits, but it's incredibly labour-intensive).
Looking at the scans from our 3-week holiday in New Zealand in 1974/5, where I shot two rolls of Ektachrome and 3 of Kodachrome, I don't think there's a noticeable difference in the quality of the results. But then, NZ rules!