I would go for MyBB because PHPBB is just full of bugs , it looks apposlutly terrible and they are really trying to hard to be like vbulletin but the free version , it just does not work for them....
Vote: Mybb. I think shese de best free forum script. - Simply design (easy to make a mybb forum theme) - God support on mybb or any language. - Is friendly with users. - Seo Friendly .