Vertical style offers a cleaner modern look like what you see in modern disc based game boxes. The front artwork receives minor cropping to fit the aspect ratio.
Retail style tries to get as much of the original box as possible by maintaining the original horizontal layout. This is less practical for display/storage, but looks much closer to the original.
We have a limited selection of titles from the Japanese Super Famicom lineup. Art for Super Famicom can be vertical or horizontal as there was not a standard layout. Art quality and availability is subject to what we can find, which is more limited than the English versions.