Mineral oil for me :thumbup: Food safe, it's cheap, and I haven't had a problem yet. I store my most of my knives in a plastic container out of their sheaths. If I haven't used any particular one in more than a month or so, then I wipe it down again with Mineral Oil. I don't know anything about oil staining though.
ETA: However, One of my favorite go-to knives is in O1 and stays in a kydex sheath on my nightstand. I usually oil it before putting back in the sheath. I took it out last weekend after not using it for 2 or 3 weeks, and rust had developed on one part of the blade. Some of the rust had dissolved into the surrounding mineral oil, and there was even a little bit of pitting. I'm guessing that the knife wasn't completely dry when I oiled it and put it back in the sheath...or the sheath itself rubbed some of the mineral oil off somehow, allowing some rust formation. I don't know what else it could have been since mineral oil seems to protect my other knives just fine. Looks like I'll start storing that one out of the sheath too....