Well, if you're looking for an unbiased view, you're probably in the wrong place ;-)
Can anyone provide links to independent tests or even comparisons of the two?
Just some quick notes: PostNuke can probably claim that it has more features / add-ons. The question is - which of those do you really need?
The one weak spot of Geeklog here is the forum. There are several solutions to more or less integrate forums (namely phpB, but they're not too easy to install and maintain (from what I heard - I'm using my own half-baked "integration" with YaBB instead).
There's also an effort underway to develop a new forum specifically for Geeklog. Have a look over at gxblock.com about their progress.
Geeklog has been around since 2000 and has always had a focus on security - you might want to check out the history of PN under that aspect ...
Hope that answers at least some of your questions.
bye, Dirk