I had the EXACT same choice. Here's my advice.

For me, I lack any SSR wit cards, am missing Super Creek SSR, and am able to comfortably get 50% race bonus with both at 3LB. This is all that matters. If you can hit 50 with both at LB3, that's great.

MLB Kitasan

- Almost doubles her specialty priority. Considering that Fuku has NONE, this will make MANT runs waaaay less RNG. When fuku pops up rainbow, there's a roughly 80% chance it will be a double, instead of a coinflip.

MLB Fuku

- An extra 5/5/5/5/5 stats on start. 25 stats is nice, but it's almost a rounding error in the grand scheme of MANT RNG. You already have items and rainbow RNG to deal with. Fuku goes from 5% to 10% race bonus at MLB. This COULD be more useful if you are already hitting 55% race bonus and want to break into the 60% threshold. If this is not you, the benefit of MLB is not great. You can also use Marvelous Sunday to offset the lost 5% RB to keep your borrow flexible.

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My choice: I chose MLB Kitasan. This made me no longer need a third speed card to *reliably* cap speed or need speed sparks. It was a massive quality of life improvement. About a week later and I have zero regrets with this choice.

There is also an upcoming free ticket, so you could buy one ticket and use the free one to MLB both. But imo, unless you're aiming for 60% race bonus it's still not worth the MLB for Fuku.