I booked for the new area, we moved when I was about 34 weeks.
If you want to talk through labour, birth and options then the NCT class is great for that, so if the cost isn't an issue then I would go to the one near you anyway. But you're right, the social aspect is probably the main reason why people pay for the courses and I prefered going to the course where I was going to live, so I knew people in the area.
Do you have any idea when you might make a decision about moving? I'm just asking as I actually found the whole move quite stressful - not the move itself, but having to change doctors and midwives and hospitals and everything so near to my due date, I had a lot of problems seeing a mw at the right time after I moved and ended up not having a hospital tour or really knowing anything about the hospital until I turned up in labour. No reason why you would find it so stressful, that was me panicking, but I'm just thinking about all the other things to organise as well as making friends.
However, as someone who moved to a brand new area with no friends at all just before having a baby, I've made a lot of friends separately from my NCT group. You can meet people online on the local boards here and also on the rival site's messageboards, sometimes the NHS runs free classes where you meet other new mums, people are friendly at baby groups etc., the NCT often have Bumps & Babes groups where you can meet people too.
But calling the NCT to ask their advice would be sensible too.