WP, but not by a whole lot.
Honestly when it comes to basic integration there’s absolutely no difference. WP and WPMU are the same codebase after all. The only real difference is whether or not you want your blog owners to be automatically added to your primary blog and by proxy as members of the forum.
Deep integration is accomplished exactly the same on either platform too. Just stick with µ, eventually (as in anywhere from tomorrow to 2017) the two will merge anyways and if you install a second copy of standalone WP.org for your forums, you’re just going to wind up with two µ’s down the road.
I noticed you tagged this convo bbmu, just so you know (you probably do) but when you integrate bbPress with µ you don’t get bbPress µ as a result. When /bbpress is accessed, no matter the blog, the viewer will get the exact same forum.
@mwaterous: thanks for the explanation. My basic need for integration is to provide users a single logon, plus a consistent appearance between the blog and the forum.
Does BB need to share the mu database for mu accounts to be recognized by BB? (I tried without a shared database and bb didn’t recognize a mu user.)