I was particularly interested in WowBB because their site is so user friendly (easy for me to understand) and they have all the features I'm looking for. But I searched this forum for WowBB and came up with nothing.
The sites of the other suppliers I have checked out like vBulletin frightened me away.
I would personally recommend a relatively new forum software called MyBB (no affiliation). It is free and open source. It has been accused of ripping code from vBulletin and IPB, but after looking at the source code these allegations are untrue.
It has more than enough features, and is extremely user friendly with great support and mod sites.
It is currently at Release Candidate 4 in its version. I would wait until MyBB gold version is released which should be any day now. I will sticky you the URL.
To reply in more general terms... if you see a forum package that you think looks good, do a detailed review of the features/requirements list to see if it can do what you need and whether it will run on your server.
The next stop I usually make is the forum's own forum. I look for what kind of problems people are reporting and how quickly a reply is received. If you see posts about installation problems languishing for days, you can expect to have difficulty getting support if you need it. Also look at the quality of the replies, i.e., do they come from the authors or support team? Do they usually get the answer right the first time? Overall, look for a busy, vibrant community.
The next stop is to look at the hacks that have been written. You won't need most of them, but a good base of existing hacks suggests that if you find something you need down the road, it may already exist or there will be someone you can hire to write it.