I did an archive and install, but then realized I had a significant pile o' apps (plus libraries) that I'd accumulated for no good reason - basically out of curiousity as I browsed Versiontracker or just heard people rave about things here at MR. So after a couple days I saved that "previous systems" folder to an external disk, and then did a clean install.
Both systems worked just fine, and I didn't really see any speed differences between the two. Advantage of archive and install is, of course, that you don't have to manually bring back your keychain, iPhoto library, iTunes, etc. etc. Main reason I can see for a clean install is if you tend to play with a lot of apps just out of curiousity, and so tend to tie up a lot of extra space for no good reason.
If you've used haxies or similar sorts of system modifiers, then I'd say most certainly do an erase and install. But most people probably don't do that (I'm not talking about adding preference panes and the like; that's all pretty safe).