Join, any shared plan with basic features will do for forum hosting unless you want to have a lot of members on board at the same time (How many do you plan btw?) If the number of members exceeds the number of simultaneous MySQL connections allowed on the host's server, see it in the TOS or in the Abuse Resource Policy as I have it with ahosting.biz whose shared I use at the moment.
http://www.ahosting.biz/legal/rap.html