Did anyone use Kodachrome? Was it only a slide film?

Whatever was cheap. Some variant of Kodacolor, probably; Kodacolor VR in the 90s. "Popular" for Kodak would mean whatever people were taking snapshots with.

If you're talking about "Photographers" rather than folks taking snapshots of their kids at Disneyland, I suspect most of them were shooting Fuji during that time. Not that Kodak didn't have a few well-regarded professional films, but Fuji had the mind-share.

--
The open-source LightZone Project: http://lightzoneproject.org/