Fresh.
Because some programs will be upgraded and that process will not work in all cases (if you go from, eg, squid 2.4 to squid 3.0 and the conf is wildly different between the two, what do you want it to do with the .conf file? Both answers are wrong.) you will have a load of trouble if you ugrade, particularly over this this large a gap from start installation to final inst.
Over a 0.1 gap from old version to new version
and if you have few services running, it might just be faster (but a bit risky) to do an update rather than a clean install, but in your situation neither of those is true.
In addition there will be changes of default program from the start installation; I can't remember what used to happen about networking back then, but I'm pretty sure network manager wasn't in existence (and it may still not be entirely a good idea, but that's not the point), I think that the automounter went through quite a few iterations around 9.0/../9.3 and I'm sure if I knew what services you use on your server I would come up with a few more candidates for things that will go wrong, eg, Bind.
Have two copies of all important data! You don't want to be completely reliant on one copy and when you have finished send one copy to the fireproof safe/offsite and keep the other somewhere more easily accessible.
