1. Support

Nothing beats vBulletin's support team. They've got an item on their website that shows their response time for the last 30 issues - it varies from an hour or so to a few hours. Not only do you get the quick replies, you also get proper replies that explain all the possibilities.

2. Community

There’s a huge community of vBulletin users who create hacks and lend a hand. If there’s something you need for your forum, chances are it already exists.

3. Performance

Reason many big sites run it is that it doesn’t fall over on its knees (like some other systems) when you’ve more than few users online at once.

4. Features

Comes with a huge number of configuration options – it’s extremely flexible in how you set it up.