Decision theory A is by far preferable to me.

Of course, that's assuming that by newcomb-like scenarios you only include those were one-boxing is actually statistically correlated with greater wealth once all other factors are canceled out.

If Decision Theory A's definition of newcomb-like included a scenario where the person was doing well enough to make one-boxing appear to be the winning move, but was actually basing her decisions on hair-colour, then I would be more tempted by Decision Theory B.

IOW: whichever one wins for me :p