NHS classes in my area: one day at the local hospital. No really opportunity to chat. Good, basic information given out by hospital midwives. Although a photocopied sheet of contact details was passed round, no one bothered.
NCT classes: went over several weeks during the evening, so you got to know the other couples. Excellent teacher who took her job really seriously and made the classes fun and interesting. Afraid it really was the cliche of 8 middle class, professional couples (er, exactly like me). Everyone had gone in order to make friends (one person even said at the first class, when the teacher asked what we wanted to get out of it, that she was "paying for posh friends"!). So everyone made a real effort to get on and arrange coffee / lunch dates etc when we were on maternity leave, and then when we had had our babies.
I honestly think it was much better than just meeting people at baby massage etc because you meet people who specifically want to be your friend, and who you are likely to have lots in common with and get on with. It's quite hard to go up to someone at baby massage and invite them for a coffee - it's kind of like dating!
And my experience of the quality of information and teaching by the NCT was really positive too.
I am still in contact with all my NCT friends from my DD (born June 2008) - we have a joint birthday party for all the children, and a joint Christmas party too (complete with one of the dads being Father Christmas), and we regularly meet up in various combinations. I would count some of them as good, hopefully life-long, friends.