We've upgraded many of our Macs this year. Basically, all new iMacs. It's been a few years since our last across the board upgrades, but in the past, I've always used the OS Disk to erase, partition, and do a fresh install. This time, there is no disk. My question (aside from partitioning the HD) is better to do a fresh install of Mavericks (saved a bootable copy on usb drive which has been tested on an older Mac to ensure there's no corruption), as opposed to upgrading through the app store? Thanks!