As Steve says.... the disc is the better buy. If your computer goes belly up like mine has you could lose the download. Yeah you can redownload it but why when you could have the disc. BTW.. I'm old too and prefer to have the disc.
I'm running Windows 8.1 now and SH5 installed just fine. Even the Ubisoft folder is outside of the Program Files where it should be. Haven't played it yet as I need to get my mods back in first.