I want to make a new mono deck and I'm trying to decide on Uppers or Montana. What holds me up is mainly the bonus. A -10 min.3 is great but a -12 min 8 is great too. What lacks in Montana is amazing stand out cheap 2* but there are needs in Uppers too. I focus on 2* and 5* because those are usually what makes the best deck when both of those are great.
Actually, the Uppers bonus is hella better than the Montana bonus. -2 attack isn't a game-changing difference and it's a worthy price to pay so you don't need to pill to get above your own minimum.
That being said, the big deciders for your dilemma are still the two posts above me.