PunBB vs ExpressionEngine Forum

I plan to create a web journal (not in expressionengine) and am going to be including a forum on my site.  Part of the forum will be used for discussion of my blog entries (every entry will have a link at the bottom to a forum topic about that entry).  The rest of the forum will just be for general discussions among my visitors.

I am debating between using punBB and the ExpressionEngine forum module for my forum.  Could anyone give me advice on which is better?  I know people may be biased here, but hopefully some people can give me objective analysis.

I especially want something with straightforward CSS styling so I can tightly integrate the look of the forum with the look of my site.  For example, I’m looking to have all the user control/registration/login links in a sidebar, and not at the top of the page.

I also want the software to be lightweight and simple.  I want there to be no spam.  In terms of the amount of features, I think both punbb (with extensions) and EE are adequate.

What are the relative pros and cons of each vis a vis the other??

Thanks in advance for any advice you can give me!