I know it may seem straightforward for most people. However, it was not as straightforward for me. So these variations and their descriptions are as follows (will update if a better description comes along). Better descriptions can be found under the checklist drop down menus in a blue box
90 Baseball variation - When looking at the hologram baseballs appear.
90 comic ball variation - When looking at the hologram carrots appear (based on Looney Tunes) with a small 90.
90-91 hockey sticks - When looking at the hologram it looks like an X with 90 in a block type numbering.
91 Upper Deck variation (base) - When looking at the hologram you will see super small 91s appear throughout the hologram.
92 Upper Deck variation (futuristic) - When looking at the hologram you will see the diamond Upper Deck logo.
When life has you down buy a pack of cards and realize you overpaid.