If your worried about moving to another platform, just do like I did and install XAMPP on your local drive then copy the entire forum and database and convert from there. I know there are tons of converter tools for PhPBB, vBulletin, SMF, UBB, IPB, MyBB, XenForo, etc, etc. SMF is nice because of the hook system when installing MODS, but it tends to be pretty taxing on the SQL. My personal preference would be PhPBB because it is so easy to work with. I've had no problem at all creating my own MOD's for it, even have a couple of them listed in the PhPBB MOD database. Not to mention there are tons of theme's available for it, and creating theme's is a breeze too.
One of the forums I owned had 500 plus sub forums (newsucks500.com now under new ownership and new platform), which, on most any other software, can really overheat those SQL database tables. PhPBB was able to handle it all just fine with no slowdown or crashing. Something I never would have attempted with SMF. In fact, the largest forum on the internet (gaiaonline.com), is nothing more then a heavily modified version of PhPBB.