I don't want to deal with Kodachrome 64 anymore. Too easy to get gray pictures in less than perfect light. I'd rather use E100GX for slide film in that speed range. (Oh, right, they discontinued that! Starting to stock up on 81A filters to allow using E100G.)
Kodachrome 25 was wonderful, I bought three frozen rolls a few years ago, and got quite a few "keepers" from shooting them.
I bought some of the last Kodachrome 200 at Calumet, newest they had (still in date), kept it frozen, and have shot one roll. Shifted magenta -- the last rolls Kodak shipped were on the hairy edge of expired. I've also had overexposure on the last two rolls of Kodachrome 200 I shot, both in the same camera (Leica IIIa) that exposed Kodachrome 25 perfectly. I don't get that. I think I'll shoot the last two Kodachrome 200's on my Topcon Super D, it's always exposed Kodachrome reliably. Since I have Kodak PK36 mailers, need to do that by the end of the year. The only really happy experiences I had with Kodachrome 200 were with the professional version, the amateur version was hit-or-miss at best.
When the two rolls of Kodachrome 200 are gone, I'd say I'm done with Kodachrome. Unless someone offers me frozen Kodachrome 25 at $7.50 a roll. (Not likely!)
Most likely when I want the high-saturation look, it will be Ektar 100. While I can still get reliable E-6 processing, I don't know how much longer it will be available.