Joomla offers the most expansion capabilities, but I think it's hard to beat WordPress for a standard blogging frontend. I've seen some implementations of WordPress front-ends with vBulletin forums. Not sure how they are integrated, but it's certainly happening pretty often, so it cannot be that difficult.
Joomla definitely has a learning curve. Still very pesky. Even after all these years, I find myself scratching my head. The add-ons don't help matters. Building a new site from scratch and realizing how much actually goes into my sites.