Depends on your budget, If your forum is small / new you don't need a VPS straight away, shared hosting is fine. However if you are set on a VPS legionbox seems to offer more bang for your buck however i have no experience with either so cannot comment on performance.
I have been with HostingSource.com for over a year now and they have been nothing but great.
I am totally impressed with these guys. I just hope they don't grow too large and lose the foundation that is making them so impressive.
QHoster.com and libertyvps.net VPS accounts are noteworthy due to their unmatched services.
I am happy with their services and will recommend them to anyone looking for good hosting at affordable price.