Something else to think about in finding the perfect writing group is the organisational side of things. How often do they meet? Is it going to be too often or not enough for you? Most of the groups I'm in or have been in meet once a month, but Western Women is weekly, and SuperNOVA is talking about having a second, different kind of meeting every month, largely thanks to Ellen who came up with the brilliant idea of having a novel-writers' get together to talk about writing. For those of us not keen on workshopping, this is a Godsend. There's nothing I like more than getting together with writers and talking about writing. (Oh, except for writing, of course!)
Something else that affects organisation is the size of the group -- and this can dictate where they meet. Western Women used to meet in the Footscray Community Arts Centre, which was great when they had us upstairs in a gallery, but gradually we were "downscaled", first to a room in the dungeon (which I quite liked), then to a room where the potters met to make things, so the benchtops were often slathered with wet or flaking, dry clay. This didn't work nearly as well. Western Union used to meet at people's houses, but then the group got too large and found a space at a neighbourhood house, but many didn't find the atmosphere as convivial, so the group eventually went back to meeting at houses. Similarly, SuperNOVA (in its old Nova days) used to meet at a pub in Williamstown, but as it got too large it too moved to having meetings at people's homes, which works better for them. Melbourne Writers met at the Bailleau Library at Melbourne Uni -- this group, with about 80 members, was far too large to meet at people's homes, which is not to say 80 ever turned up for a meeting while I was there. Meetings seemed to average 15 to 25 people, but this brought in another set of considerations, because you had to book your workshop place months in advance, and the month before you would duly bring in 30 or so copies, hand them out, only to find the following month that only about three people at the meeting had attended the previous meeting and so had received your story, and the other twelve had never read it and had nothing to contribute.
SuperNOVA is another big, sprawly group, but one that eschews the regimented organisation of Melbourne Writers Group and tends towards a more anarchic approach. No booking schedules for crits. No hard and fast rules about when meetings are -- well, there are supposed to be hard and fast rules, but there's often someone who will say they can't make a particular meeting and ask if it be moved. The answer to this question should be no. Especially in a big group. But it often isn't. Then there is an awful lot of to-ing and fro-ing about when and where the meeting's going to be. Sometimes so much so that no meeting eventuates. I know it drives some of the more organised members balmy.
Another consideration is the politics of the group. Does everyone write the same kind of thing, for example, in SuperNOVA it's speculative fiction (science fiction, fantasy, horror)? If you're writing something outside of this genre either often or occasionally, are you going to be able to workshop it? Mostly, people are workshopping SF in SN, but occasionally someone will apologetically ask if they can workshop something outside the genre. I don't think they should be apologetic. We should all use our writing groups as best we can -- and while people may not have the writing or even reading experience outside their genre, we are all experienced readers, and can comment on things like characterisation, setting, words on the page etc. Nothing annoys me more than people who say, "I don't read this kind of story, so I've got nothing to say." That's a cop out. Melbourne Writers had a preference towards more literary fiction and poetry. In Western Women, I'm the only spec fict writer, though Sherryl does occasionally dabble. She's the only crime writer. When I first joined, they all seemed to be writing poetry, and I told them I didn't write poetry. I had no intention of starting either, and now I've had more poetry published than anything -- so a good writing group can expand your boundaries, as long as you leave yourself open to the possibilities.