Well, personally, I don't mind the type of forum used, as long as it's concise, easy to read, and it gets used. As a regular forum user (not just me, but I mean in general) I don't think te way it's constructed matters as much as the content.
Invision Power Board - best board in my opinion
ProBoards - simple and free and does the job.
Invision. Heard nothing but good things, seen nothing but good things. Fully customisable. Beautiful.
Proboards. Down almost everytime I try to visit their website. 'Nuff said 
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vBulletin and Invision are my favourites, although phpbb can be customised to be really nice, plus it's free.
Simple Machines Forum - without a doubt.
I love vBulletin, enough that I bought one. I pretty heavily checked out the other options when I did so, but really liked the look of vB best... and there's a fantastic community of people producing mods for it. I found it did everything I wanted, and I've never had a single problem with it - plus, it was easy to install and update, despite my being pretty clueless. I even managed to install a load of mods despite having no idea about PHP and so on, and my understanding is that in the newest version makes things even easier to do.
I'm pretty sure you can preview the admin side of things for the various paid ones out, and it'd be worth doing thing. I remember looking at test versions of Invision and vB when I was deciding which to go for.
I've noticed a few whinges about UBB on these boards, and I need to put together a messageboard for work - preferably one that's easy to link to individual channels with.
What's your favourite flavour of bulletin board?
Is it time for the dance of joy yet?