There are lots of opinions on what the "best" stock finish is. I like oil finishes myself. They just have a more natural look than varnish, polyurethane, etc.
One of the nicest and most idiot-proof finishes I've used is Birchwood Casey's TruOil. It really does a good job. I've used it on at least 20 stocks over the years with good results, and just did another this week. It does take a few days of application and buffing between coats, but it's effort well spent. If the stock happens to get scratched, it's easy to touch up with no need to refinish the whole thing.
One thing about TruOil though - It's not waterproof. If the stock might get wet, Birchwood Casey also has a sealer/filler that helps keep moisture out. It's applied for the first coat, with TruOil applied on top. It works very well in my experience.