Yeah, because of the 2 piles drain from ruins and curses, the game is most likely going to 3-pile if both players go for the junkers. If the game is going to 3-pile, a curse in your opponents deck is going to go a lot further than the ruins, which can be marginally helpful sometimes. It depends on the board. If there was Upgrade or Junk Dealer, I might pick up Marauder just to get to the trashing cards faster, however I think I'd still open Sea Hag, due to the top-decking of curses, as well, its a guaranteed hit, whereas Young Witch can potentially be baned.
So basically,
strong/mid trashing: I'd open sea hag and pick up a maurader later, (or if 5/2 and one of the trashers is 5 cost, I'd pick up that instead)
little to no trashing: sea hag, young witch and mostly go for money, maybe pick up a marauder down the road to help the piles drain.
It also depends on how many people are playing. I played a 5 player game with Marauder and Witch that ended on curses/ruins/estates. It was pretty brutal, since you could get 4 junk cards in your deck for every card you bought, until the piles drained, but then you're looking at 1/3 of your deck being worthless.. pretty hard to build off of!