Who won a Game of Bar Dice?
Jelly, 17 14 bytes

ċⱮ6Ḣ©+$®aĖUṀ)M


Try it online!

A monadic link that takes a list of the two lists as its argument and returns [1] for player 1 wins, [2] for player 2 wins and [1, 2] for a tie. TIO link tidies this up for display. 

Thanks to @JonathanAllan for saving 3 bytes!

Explanation

            )   | For each input list (e.g. of one list 1,1,3,3,4)
ċⱮ6             | - Count each of 1..6 (e.g. 2,0,2,1,0,0)
      $         | - Following as a monad:
   Ḣ            |   - Head (number of 1s)
    ©︎           |   - Copy to register
     +          |   - Add (e.g. 2,4,3,0,0)
       ®a       | - Register logical and with this
         Ė      | - Enumerate (e.g. [1,2],[2,4],[3,3],[4,0],[5,0])
          U     | - Reverse each (e.g. [2,1],[4,2],[3,3],[0,4],[0,5])
            Ṁ   | - Max (e.g. 4,2)
              M | Index/indices of maximal score