x2 -- we have both in my city. The Critical Manners ride has the positive effects of forcing drivers to realize that there are, in fact, cyclists in the city and that we do, in fact, have the same right as everyone else to use the road. Critical Mass here isn't as bad as it is in a lot of other cities
(partially because there aren't enough participants for it to actually reach 'critical mass'
), but there are still the occasional asshats. Critical Manners is a much smaller ride yet, but it doesn't cause the rage in drivers which will then backfire on me, when I try to commute in the morning.
However, even Critical Manners is not a panacea. Its success is predicated on all the participants actually understanding and following the rules of the road, and at least here, the ride leaders aren't very good at enforcing the rules in the back of the pack. There are sweepers, but they always tend to miss the last few stragglers
(who are the least-confident cyclists, needing the most guidance, and the most likely to do stupid stuff because they're afraid of getting left behind
). I actually almost got run over as a pedestrian by our local Critical Manners ride, when a couple nitwit girls on cruiser bikes, no helmets, and flip-flops, decided to ride down the sidewalk because the shared bike/car lane was too scary. I yelled at those girls, who then yelled "F--- you, you aren't a cyclist, you don't understand!" At which point I just burst out laughing.