Well I was in the same position - had decided I wanted to go for one of the
two.  In the end the EF81 won out as it is a lot more pocket-friendly and
(IMHO) looks nicer too.  I really like it so far and I have no regrets going
for it.

One of my friends recently got an N80 so I've been able to have a play with
one of those too, and while it's certainly feature packed - it is somewhat
bulkier, while the keypad is actually a bit more fiddly.

I guess it really comes down to whether you actually want all the extra
features of the N80 or not?  Is Wi-Fi important to you?  3MP cam with flash
rather than 2MP without?  Full Symbian OS?  If the EF81 does everything you
want to do anyway then I'd recommend that over the N80 as it is a far more
discrete package and still looks the bee's knees.

One thing to bear in mind though is availability - while the N80 is being
sold almost everywhere (stock allowign of course), the EF81 has initially at
least been a phones4u exclusive on Vodafone - so you haven't been able to
get it anywhere else in the UK.  I don't know whether that exclusive period
has ended yet though (I'm sure it will in time - CPW have had it as coming
soon for months now).