I think what it comes down to is what your long term expectation is for appearance.
If you just want to put something on it to give it a finished look and keep the occasional oil or paint spill from seeping into the wood, personally, I'm a fan of finishes that can be repaired easily. Boiled linseed oil, Danish oil, heck, even mineral oil would all do a good job of keeping the wood from absorbing spills. They won't protect the surface from dents or scratches, but should you want to touch it up, it'd only take a few minutes.
Now if you want to keep the butcher block looking like new, that is a whole different story. As mentioned already, poly would probably be the better option. But even then, will require maintenance.