Yup, it's hard to make blanket statements about colour and/or tonal accuracy of any of these because they have plusses and minuses.
Astia has the broadest exposure and colour-temp latitude and that's why people usually get results with it that the consider more accurate. If you are new to slide then astia is a good place to start.
But the others (and 64T) are capable of accurate colours under certain lighting conditions. I mean, for the very best colour accuracy in product shots, I think 64T plus tungsten lighting is tops! But obviously that just isn't practical for many applications.
If colour accuracy is a major issue then one uses a colour meter and filters and the whole bit. A lower-end solution would be to include a colour sep chart in a shot as a reference so that you can adjust later.
What's your subject, what's your light?