Hi,
If the forum you want to use is MySQL based be sure and read the reviews for each and make sure it's available... I didn't read all of them but most seemed to include it as a database choice.
If your forum is a successful one and generates a lot of traffic, as you would hope it would, your main concern may be the "Bandwidth limit /month" spec. There is nothing worst than trying to use your site one morning and getting the dreaded "Bandwidth Exceeded" message - rendering the site useless for the remainder of that month.
So with that in mind get the package with the most allotted bandwidth per month once the storage and forum requirements (MySQL/PHP) are met.
Sorry I can't help with the actually selection process - I'm not familiar with any of those particular sites. :/
Good luck!
Daf