I have spent 25 years on a farm, fixing things. Usually when something is stuck, the best socket is a 6-point instead of the more common 12-point socket. A 6-point has flat places that line up with the bolt. When things are very rusted/stuck, you can still round it off. This model of Vicegrips is absolutely the best there is. It hold three flat sides, and you can tighten it up to "crushing mode" if you are not careful.
As mentioned, these are not as much of an "all around" tool as other models of Vice-grips. My personal daily favorite is a 7WR (7", rounded jaw, wire cutters). This 7LW is a specialized model, mainly intended for removing stuck bolts. Since all bolts still maintain that same geometry, this works equally well on SAE and Metric nuts/bolts.
Yes, use penetrating oil. Yes, use a torch if you have it. These 7LW are still what you need to grab on to a stubborn nut/bolt.