From personal experience I recommend using a free host such as web000 and using an open source forum software (or pirated) and doing it that way. This way you are not restricted with your choices but if you do go in this path you have to consider a lot.
Of course it sounds like a no brain deal but consider this; DB errors, designing of the forum, configuration, maintenance, learning how to use FTP, eventually paying for hosting (if you want a custom domain), etc.
Now if that doesn't sound like your thing then go with a free forum host, Forumotion is recommend just keep in mind that in the future if you become bigger and have to move hosts you can forget about your forum and start fresh because they will not release their database to you.
As far as Forumotion goes it has it's pro's and con's. A few pro's being you don't have to pay for hosting, maintenance, user friendly, easy to configure and make look pretty, free domain name (once you hit a certain amount of activity) and you won't have security issues.
In summary if you want to put less work into the forums then go with FM but if you plan on it becoming big and what not then go with something else. In my honest opinion FM is the best.
EDIT: Clan thing?