sjgslack
Established
I'd go for the M6 over the M2, especially as a first M. Metering (You can ignore it and remove the battery if it distracts you), standard flash sync port if 1/50th flash sync is your thing, more framelines (Some would disagree with me here, but I feel it is an advantage), the quick loading in the M6 is helpful and it's just a fantastic camera.
The M2 is a seriously smooth camera though, feels as close to a tank as you're going to get with the M system (The m4-m6 don't feel fragile, but the M2 just feels extremely solid) and is extremely fun to play with, perfect if you don't think you'll ever need the 28mm, 75mm and 135mm framelines in the viewfinder - though you can just use the entire viewfinder if you're shooting 28mm. But I think I'd always grab my M6 first when shooting, if only for the metering
Of course, I might be totally biased because I love my M6 to bits and the M2 I sort-of-but-maybe-don't own has been tripping over its feet as a backup camera right out the gate because I made poor decisions sometimes. Your milage should vary though.
Interesting about the frame-lines. I currently have a 35 and a 50, but a 28 or 75 are certainly things I may think about in the future......