Pros and Cons
So to my understanding a well tuned finish plane will blow a sandpaper finish out of the water. Personally I’m not sure I would touch up your workbench top but I also prefer a rougher top, so I hope to get a toothing plane to rough the surface of my workbench I’m building.
Personally, I think I would use a joiner plane like Stanley #8 or wooden one if you have one. That way you clean the top but you make sure it is very level and square. Then if you wanted to add roughness after cleaning you can use a toothing plane, plane perpendicular to the grain, or use Paul Seller’s toothing plane (a section of saw blade in a board) to add some grip. All of that is just personal preference on what you want the top to be like. I like mine to have grip.
I think the smallest plane I would use would be a finish plane like a Stanley #4. I’m simply thinking of time and effort here as well as a bit of keeping the top square. I would think it would take a long time to clean up a workbench top with just a block plane. In any rate I would use a bench plane of some kind. The long work of moving a plane against that much surface will definitely ware out your arm just using a block plane.
As far as sandpaper, if you have like a belt sander with a medium grit I’m sure it could also knock off a layer pretty quick. You will have the issue of making sure to remain square as you sand. If you want a rough surface on the top you can just use a higher grit. Personally, I don’t like all the dust or vibration on my arms. I feel like a plane takes less time to but that may just be because I enjoy the use of a plane and don’t enjoy the use of a sander.
All in all there are a few good options available.
Hope my opinion helps.