Which Muk would you power up?
And before you say, "Neither, both are bad investments", let me tell you, it's my stardust and I'll spend it however I want!
I have a pair of 96% Muks (one regular, one Alolan). If I gave you plenty of stardust and candies and told you to spend them right now on one of them, which would you choose, and why? Also, which moves would you pick?
Answers
The "doesn't resist machamp" thing is the biggest thing holding A-Muk as a defender. But I wonder if seeing a big A-Muk in a gym would cause people to overthink things and try to switch to something like a Psychic Mon (for the less intelligent) or unpowered Groudon or something like Rhydon. I find that most of the trainers in my area are either not very knowledgeable about optimal counters or too low of a level for it to make much of a difference. This makes me think that the Alolan version's unique typing would be better.
Short answer: Kantonian Muk. Go nuts.
Long answer: The fact that Alolan Muk got Dark-typing means various things: It's double resistant to psychic, however there's a lot of Pokemon that fill that role better (Tyranitar, houndoom, even Absol).
On the other hand, Kantonian Muk pure Poison-typing gives him resistance to Grass, Bug and Fighting. So, it will be a great choice for Gym defense and for Tangela raids.
