Between MyBB and phpBB the answer is quite easy to me atleast.
Go for MyBB it simply is better designed, has good plugin support. And a bunch of nice plugins. The support is quite well from the community to so.
With the 1.8 update up ahead it will even be put into a modern jacket get jQuery etc.
There are though, some things for me atleast lacking. MyBB really is a forum software. While you can use the default portal this isnt the best thing designed compared to other forum software. Especially looking at SMF simple portal plugin, which is far superior to the MyBB portal.
Depending on what your looking for you need to choose i guess is the right answer.
- Are you looking for a great forum software with an okay portal go for MyBB.
- Do you want a forum with "okay portal" plugin and lots of game related plugins/themes, go for phpBB.
- If you are looking for a really good portal plugin with a good forum go for SMF.
But thats just my opinion and ofcourse doesnt reflect other people's opinion.