What is the rarest attax card of all?

The rarest Attax card is often considered to be the "Messi 101" card from the Topps Match Attax series, particularly the limited edition versions. These cards are highly sought after by collectors due to their rarity and the fame of the player. Additionally, certain promotional or event-exclusive cards can also be incredibly rare, depending on the specific series and year of issue. The value and rarity can fluctuate based on collector demand and market trends.