Just like it says in the the title. I often enjoy the grain in BW film, but rarely think that it looks that good in color film. However, I have also noticed that some grain seem a bit more "blurry" and other sharper. This may have been one of the nice features of the old Kodachrome for instance. So which one do you think looks best today? (slide or negative)
Same here, grain in BW often looks more pleasing to me than in color. Therefore I generally prefer the finest grain in color, which means color reversal film, as it has much finer grain than color negative film (because in the reversal process the more bigger silver-halide crystals exposed in first exposure are removed and the final picture consists mainly of the smaller remaining crystals of the second exposure). Provia 100F is therefore my most used film, followed by Velvia 50 in the cases I want a bit higher color saturation.
When using CN film, I go mostly for Superia 400 when I am using amateur film, as it has finer grain than Ultramax. C200 has finer grain than ColorPlus 200. So far for my budget options (mainly family snapshots).
With professional CN film I prefer the very fine grain structure (and more natural colors) of Portra 160.