I've been to many different parties over the years, good, bad and indifferent.
I would recommend LMP for the first timer as, while it is not the cheapest, it has the best girls and the best chilled-out friendly vibe.
First off, unless you tell them, no one else will know if it's your first time. I didn't saying anything on my first time and had a great time. From other people's feedback, if you tell the host (Emma, Lady M) it's your first party you might get a bit more attention to make sure you know the ropes and are comfortable about everything.
LMP is not a cliquey place (unlike some swingers parties, if you're comparing them) and you can easily strike up a conversation with the other guys. Just ask them if they've been before, what other parties they've been to, favourite girls etc.
I've partied with Chantelle before (not at LMP but somewhere else when she was just starting out in porn). Great fuck but bear in mind porn is always over-acted so don't take her videos as gospel. I'm not sure it's a good idea to go to any party 'really, really interested' in one girl in particular. At best, you will spend too long with her and get ticked off for hogging her. At worst, you will get frustrated seeing her in action with other guys and neglect the other great girls there.