http://forums.pelicanparts.com/1-porsche-technical-forums/ or http://forums.rennlist.com/ or http://www.porsche356registry.org/356talk.html really depends on your specific area of interest.
Both have their + and -. (In-fact you'll see many of the people are on both, even posting up subject about both). I seem to head over to 6Speed more than rennlist myself, but the jury is still out. One thing though....... rennlist is much more on the porsche-dedicated for sure.
when considering forums of Porsches, one must remember the massive expertise found on the Pelican Parts forum.
++.......... Great point. Overall its always nice to hit all three of the sites, especially if you are looking to solve a problem. (And unfortunately you're gonna run into the person that says "search engine is your friend".........where they just could have put a link or an answer for you. Unproductive waste of time IMHO. If ya can't help someone, just dont even bother posting)
if you're a DIY'er, Pelican is amazing. otherwise, I think modern 996/997/Boxster/Cayman, it's a toss-up between 6speed and RL. anything older (incl. 928/944), aircooled, or racing-related, definitely RL.