Not so simple.... I need one who is:
a) Capable enough in the field of research that I'm tackling....
that strictly restricts my choices, because different profs are
good at different fields.
b). Someone who's actually willing and able to take on another
postgrad at short notice (and for the next 3 1/2 years)....
c) Someone I can get along with well enough for the next 3 1/2
years.....
And I'm actually supposed to meet up with my outgoing prof to
talk to some other profs together this week..... but it turns out
that he had a last-minute overseas trip. And I only found out that
he was out of the country when I tried to email him and got an
out-of-office autoreply instead.
Sigh.... honestly I can't help but feel as though I'm being left
high and dry.... 
my advice is just go to another prof. are there any you are on
better terms with? Go to him and ask him for some advice on who you
should approach. then just go and speak directly with these profs
about it.
anyway actually I don't think you need a real expert in your
area just some one who knows what's going on and can give some
advice. postgrad work should be pretty independent (wella t elast
for pdh)
