We use quite a bit of walnut. We always stain it to pull it together to a consistent color.First...why are you staining walnut?
I usually use orange shellac to warm it up but have never stained it.
I personally think walnut isn't that attractive unless the pores have been filled.
But, I'd have to go with satin regardless of filled or not. High gloss looks cheap to me and will only accentuate the pores even more.
Satin is my choice. I almost never finish anything with high sheen.