Hotel is also dependent on each persons own budget, a lot of hotels in London can be pricey - the cheaper ones tend to be further out of the centre. I don't think there's a definitive guest list atm too. I think a venue is most important - after all, people can even book a hotel wherever they would like! Some people might not be as comfortable as others being in the same hotel with members. I would honestly think that hotel is more of something that you should be booking for yourself - absolutely discuss it with others and try and book the same one, but yeah, venue probably more important at this point.