mezzo every time!
has far greater upgrade potential for less money.other than that the standard mezzo is lighter better handling and folds faster. you will see some reports that the mezzo is slower to fold.
I own both, the mezzo takes me 10-15 secounds unfold and 15-20 to fold.
It takes me usuallu at least 30 secs to fold or unfold the brompton.
Some owners stsate that the clips are difficult, again they like to be snapped it in place and once you get used to this it is a doddle.