(Puts on Wayback™ thinking cap)
Third-worst film I ever used: Kodak High-Speed Ektachrome (process E4): Granted, I tried the stuff a while after the E6 films were released, because, up to that point, the only slide films I ever used were Kodachrome and Agfachrome CT18. I was curious as to what I was missing. Answer: not a thing. Everything Kodachrome wasn't...and less.
Second-worst film I ever used: Kodacolor 400, first-generation. This film managed to outdo Tri-X in exactly one category. Unfortunately, that category was grain, as in tons of it, and ugly to boot. Throw in milquetoast color rendition and "scratchy" contrast, and you'll know why I stayed away from films faster than ISO 200 for years, even well after higher-speed emulsions actually became pretty good.
ABSOLUTE worst film I ever used: GAF (Ansco) 500 slide film. This stuff barely hit its box-rated speed (I think Modern Photography, in one of their colorful film "shoot-outs", measured a real-world speed somewhere south of EI 400), but the evil part was the color rendition: any color you like, so long as it was predominately ruddy-rusty brown. It did compete strongly with Kodacolor 400 in terms of grain, though. 🙄
- Barrett