The rub on will give a much nicer finish but you will need to do more coats, will take longer but unless you are really pressed for time it is worth it. imho. If you all ready have can of brush on. just add some mineral spirits. instant brush on. First stir a can of oil based varnish. then mix it one to one with mineral spirits and you have a rubbing varnish. Allow 2 hours of drying time between each of three coats. Wait a day then sand to 320 girt paper and repeat with 2 more coats.
The real trouble with brush on is the imperfections that happen with the thicker varnish. bubbles, brush strokes. Don't worry about the can sayinf to not thin with mineral oil. If it is oil based it can be thinned. The warring is there just for the VOC regulations.
Now if you are like me and like the Danish oil finish mix your varnish with equal parts of varnish, mineral oil, and Boiled linseed oil. This makes a great finish but I like to let it cure for at least a week in warmish conditions before use. Longer if possible.
Randy