A few general thoughts derived from past experience of organising events (wargame and otherwise):
a) NO date is good for everyone;
b) many of the people who make the most fuss about not being able to attend will not turn up anyway after you have kindly changed the date to suit them;
c) so, subject to avoiding things likely to inconvenience everyone (eg days in 2012 when Glasgow is hosting Olympic events, thus clogging up roads, trains and hotels), ...
d) pick a date that suits you the organisers. The rest of us will fall in as best we can.