Its completely ridiculous, and the most fascinating part of this to me is that she doesnt even care about +1/+1 counters specifically
Pick whichever one suits your fancy
Where it lands depends on factors such as blues ability to apply pressure, whether there are disruptable mechanics like Heroic or Monstrosity, and the quality of combat tricks and cost of removal
Otherwise, put it into your hand. Putting a card into your hand is nice, but you can literally win games by just combining Meren with Spore Frog, which you can sacrifice to prevent all combat damage for a turn - and only costs one mana
You probably won't count on Yawgmoth too much if your only concern is to draw cards, but when looking at the whole package, Yawgmoth, Thran Physician is hard to beat