im going to say that catered is more sociable. although i never lived in self catered, i do have a lot of friends who were in it, and they're all ridiculously outgoing people who make friends whever they go - so if you're quite a shy person i see you as being limited to your flat friends (not a bad thing at all, but i don't think i could have handled this). my impression of sc is that you get quite cliquey, yes you may know some of the people who live upstairs/different blocks etc but you tend to stick with who you know (people in your flat) and do what they all want to do... i see this quite limiting as if you want to meet people you have to actively go out of your way to go to the places the type of people you want to meet are.... (again, a generalisation, but this is how in hindsight, i think i would have felt had i gone with my original choice of lafrowda....)
being in penny c, i met everyone from there, everyone from randy p, and everyone from lopes as we all had the common meeting 2/3 times a day of eating. i say its more sociable because instead of going to dinner with 8/9 people you go with hundreds and get to hear the buzz of whats going on that night etc, where everyones off to. i made a lot of friends from various social groups and remained close friends with them throughout my 3 yrs. also meant i got to experience the social lives of other people!! not just stick to my best friends who are all hardcore tp weds goers!!
anyway, once again, this is personal preference - 95% of people in catered will think that thats more sociable and likewise 95% of people in self catered will think that sc is more sociable. depends on what type of person you are... as i said i'd initially applied for lafrowda but after speaking to my cousin who had just graduated from ex she was like 'god no, change change change to catered' because she knows me and knew thats where i'd have the best time....