I would much prefer to use the Pine. Ash is far more likely to split or curve, and hard to carve.

At least here in NH, pine must be sawn promptly before borers or bluestain attack the logs in warm weather. Once sawn it must be immediately stickered and dried carefully to avoid stain/fungus. Although stain won't hurt much except cosmetically. It can be part of the rustic look if you aren't fussy.

White pine is a first class wood for timber framing.

Pete