Personally, I usually set the default storage engine to MYISAM. If you have a mega high traffic forum site, InnoDB may be better because it only locks the row it's currently using, instead of the entire table, so it may make your forums a little more responsive if you're experiencing slowdowns. But it also uses a lot more disk space and memory to store and access the same amount of data. If your server can handle it, and if you really need it, InnoDB is a good engine. But for average use, MyISAM is pretty good.
---Jamin
