I vote blake as well.... RMs have been a big disappointment for me lately, and I'm having a hard time considering buying any more bags by her. the blake is a classic, and will remain a classic... if you're worried about weight, the older blakes were heavier but the newer ones are lighter(no suede lining, thinner leather).
both are beautiful bags so i don't think there is a wrong choice. i personally have only owned the blake, which i sold because it was a bit too heavy for me (i had the one with suede lining). i guess it depends on how much you carry on a daily basis. i've seen the RM MABs in person and they are beautiful - but i personally like them in bright colors (like green or blue). whatever you decide, let us know as i'm curious how they compare side by side!