None. I was already leaning towards the 6MT and have opted for them all my life.
I saw this video with the lead for transmission development at BMW M GmbH and he says "I'd take the manual every time". Here's a guy who leads the development of and knows both transmissions in and out and is giving the manual gearbox a huge endorsement.
There was no doubt in my mind after that and I have 0 regrets.