Although I think Buell was the prettiest, the first option is probably the best canonically and what I used last playthrough.

Raven Black Shire

I used the prologue tenessee walker up to the part where Hosea suggested Arthur to get a new horse. The American Standardbred from Valentine seems like a good horse. Raven black shire is just too big imo.. doesn't seem like Arthur would use it. That horse would be more of a fit to someone like Bill or Charles. On the other hand, the American Standardbred from Valentine has a pretty medium size, plus the color matches Arthur's main coat. I believe that horse is also the canonical one which Arthur uses throughout his story.

I actually stuck with the Tennessee Walker from start to finish in my first playthrough

First playthrough i used the black shire, second one I used a Ardennes because high honor Arthur on a giant war horse..yes please

I’m replaying low honor and I’m gonna stick with the white Arabian