Both are relatively easy to farm. So it depends on their exclusive drops. None of them have clearly "better" rewards but there might be some cards that you want to have 3 copies of for personal reasons.
I find Yami harder to farm. In a 30 cards deck with 3 blue eyes, each time I select the x3 multiplier against Yami I get all 3 of them in my starting hand, making my White Stone of the Ancient useless. This starting hand is less likely against Joey, or Yami with x1 multiplier.
I don't think it is a coincidence since this happened for like 3 days with no exception.
I call this, the hand of Konami
Yugi is harder to farm cause he has dark magic attack to destroy spell&trap and also magician navigation to negate your spell/trap but joey only focus on summoning red eyes only and he don't have disruption card
I FIND JOEY IS MUCH EASIER TO FARM. HERE IS MY RED RA DECK TO FARM JOEY WHEELER OVER 8000 POINTS. 11 CONSECUTIVE WIN AND WORKING 100%.
LIST OF THE DECK IS IN THE DESCRIPTION.THANK YOU. PLEASE CHECK THEM OUT
Joey is far easier to farm because he can't destroy your backrow. I'm not saying Yugi's hard to farm but his Dark Magic Attack and Magician Navigation (when in the GY) can mess with your farming decks.