For major updates and some minor updates, I do a restore to factory settings first before installing the update. For most minor updates, I do the update, but never OTA.
I prefer to download the full installation file via iTunes, rather than just the delta change file that the OTA update pushes. Just in case any individual files got corrupted, I'd rather just reload the full validated OS.
Plus, if the device is running short on storage space, I don't have to worry about clearing out the huge amount of space that the OTA updates require. In addition to clearing out the OS and app caches, restoring to factory settings also zaps out all the cruft that accumulates in the "Other" directory.