Fuji Astia 100F or maybe Kodak Ektachrome 64. However, there is less grain in the Astia, if that makes any difference, though both have so little grain it is only on comparison to see the difference.
I tend to chose E-6 films based upon desired pallettes for particular results with specific scenes or subjects. Basically, punchy red or yellow mean E100VS, brilliant blues or greens mean Velvia 100, saturated deep greens mean E100GX, and more even lower contrast means E200. Photographing people or very subtle tones would to me dictate when to use Astia 100F or Ektachrome 64.
Last time I used Kodachrome was for shots of a big band hanging around a B-29 a few years ago. One nice aspect was that the skin tones were very even, though I found the red response is more saturated than what Fuji Astia 100F gives me.
Ciao!
Gordon