Pro reinstallation: You get a clean, congruent system without the need to do any thinking nor learning.
Cons: Lots of more work need to be done, and more time needed, until all is installed again, plus things can get pretty complicated, to not miss a conf-file.
Unless a system is really f#34ed up, I would always prefer to upgrade/update. When you understood how it works, and respect some special cases, like major upgrades (to 15 for example) which you can learn about in advance, and don't have to do instantly the upgrade occurs, it's less work, way quicker and more safe to not mess things up or even lose anything.
Plus one reboot, only, if any at all, is most downtime you risk, while keeping a running system.
The feeling of updates were "unclean" must be something related to very old Windows experiences (95, 98). Those days are long over - even with Windows.
