I'd go with Boiled Linseed Oil (BLO), Tung Oil, or Watco Danish, all of which can be found at Home Depot or Lowes. However, it's a work bench. Sooner or later it is going to get scratched by something nasty, and firearm solvents and cleaners will strip it out.
On the workbench I use most for cleaning guns, sharpening knives, or other nasty activities, I put a piece of 1/8" door-skin on top. It's essentially melamine over a thin layer of hardi-board. Clean it up with 409, discard it when it gets too ugly for your tastes. As an added benefit, it's like a giant white board. I write notes in pencil on it all the time. Mine has become pretty gnarly of late, and I plan on swapping out the existing skin tomorrow. My top is a layer of ply for strength and holding, a layer of MDF for being dead-flat and heavy, and a top layer of sacrificial door-skin.