XP grinding, conquest vs showdown

SDS

Curious what everyone thinks in regards to whether conquest games or showdowns are the more efficient way to grind xp. I need 50k to finish off first inning and only get to play once the kids go to bed so trying to ensure I hit the finish line. I need to do showdowns for team affinity but I'll do that question mark map over and over if its faster... any thoughts/feedback are appreciated

SDS

Wait, the question mark map is repeatable for a dwarf?

What is the reward?

SDS

You get 3 packs when you finish it every time