Long story short: which do you prefer, a hierarchical representation of a discussion (like the comments on LiveJournal) or a single-threaded modal (like the Gamedev forums)?

Long story long:
I'm finishing up comments in the blog part of my CMS software but I'm not sure what type of thread style the comments should have. Right now I've got a hierarchical setup like flipCode's forum and LiveJournal but it's proving to be somewhat of a pain. You see, I am determined to have pretty URLs and with the hierarchical modal it is necessary to reference individual comments because comments might be nested too deep to show with proper indentation (see the LJ and flipCode links for what I mean). I dont, however, know how to uniquely ID each comment in a pretty way. These are a couple the methods I have thought of

1. By timestamp
Pros - Easy to implement
Cons - It is possible that two users could comment at the exact same time, this could be resolved by using timestamp + user ID but in either case timestamps arent very pretty and are difficult to remember.

2. By the order that the comment was post
Pros - Easy to remember
Cons - Unintuitive since comments may be posted in multiple threads in a non-linear order one thread's comments might have numbers 1, 8, 12, 13, 42. Also unless I want to add a new field to my database I'll have to calculate this on the fly.

Do either of these sound good to you? Do you have any others?

I was browsing around various blogs to see how they implemented this. What I found was that the blogs that had pretty URLs also used a single-thread modal like Gamedev's forums. This would be much easier to implement but I'm afraid that I will lose some of the structure of the dialog. What do you think?