1. Secure the panels from ANY twisting forces
2. Placing cardboard or another separator between them with prevent frame scratches, but serves no other purpose.
3. Don't stack them more than 25-30 panels high.
Whether its face up/down, or on edge only matters if you expect twisting. If, for instance, you buy cheap pallets or overload them, then a misplaced fork lift one corner of the pallet could result in a twist or bow that will stress the panel glass and frames. Putting them on edge resolves that concern, but only as long as you guarantee nothing is going to push the panels from the sides. I suspect base twisting is more common than side twisting.
Further, while nothing should be stacked on top of a pallet of panels, it can happen in the shipping industry. Edge vertical panels will withstand this slightly better, but only just slightly
Since you're moving them by hand, you can do it however you like. If I were in your shoes I'd stack them flat with corner braces and moving straps because I wouldn't be confident I could pack and stack them sideways in a secure enough way to avoid tipping/sloughing.
Just keep them from moving and twisting and you'll be fine.