The best replacement for kodachrome is ektachrome.

The best alternatives to kodachrome are rated as following:
★★★★★  ektachrome
★★★★★  velvia
★★★★★  kodacolor
★★★★  portra
★★★  ektar
★★★  provia
★★  fujichrome
★  technicolor

Your alternative for kodachrome is not listed? Suggest!
Speaking about kodachrome, one probably shouldn't forget about vuescan.

Other search terms related to kodachrome and their ratings are:
★★★★★ vuescan
You have in mind a companion for kodachrome and it is not yet here? Propose!



Google Trends

Scale is based on the average worldwide traffic of kodachrome in all years. Click on graph for more.
kodachrome
ektachrome
velvia