>>I don't want it to be a complaints area for our site

State this clearly, along with the appropriate venue to lodge complaints (e.g., customer service toll free line, email form, etc.). You'll still have to edit or remove some posts, but perhaps not too many.

>>An important point is that I don't want something that I have to constantly moderate and maintain.

Any community where users can post content requires frequent attention. Communities are never low maintenance unless they have little or no activity, and a community with no activity is pointless. If you want low maintenance, consider a blog with no comments or premoderation on comments. This won't promote much of a dialog, but the time requirement will be minimized.

>>Also, are there any preference for Forums or Blogs in terms of SEO?

Blogs may pick up links more easily if you are posting good content and pinging the blog search engines, while forums will generate more total content with less effort on your part. As far as SEO goes, a lot depends on how you tweak the software and your attention to normal optimization details in the content. Blog URLs tend to be cleaner (WordPress, for example, offers SE-friendly URLs as a standard option), but that's something you can control.

>>Something else that my decision also depends on is whether you can easily convert a Forum to a Blog or vice versa.

The concepts are fundamentally different (despite some similarities), and I've never seen such a conversion utility. A blog normally has a small number of authors, but allows comments (often visible only by clicking to a new page) by others. A forum is a more democratic structure, and normally any member can start a thread or post on someone else's thread. Posts are displayed in an egalitarian manner, with the original post no more important than the replies.