A good choice no matter which one you choose.
I've got the FZ8 and can't praise it high enough. A really excellent camera. I bought it some time ago, as soon as it replaced the FZ7.
However if I was buying now, if the extra Ł80 won't break the bank I would go for the FZ18 over the FZ8. Not because of the Face Recognition which I think is a bit pointless anyway, or the few extra pixels, but simply because of the extra zoom range, especially at the wide angle range. The FZ8's wide angle is approx 35mm focal length in old camera terms, but the FZ18 is I think 28mm which for landscapes is far more useful.
But no matter which you choose you won't be disappointed.