Who had the better slider: Steve Carlton or Bob Gibson?

They're two of the all-time greatest: Bob Gibson struck out 3,117 batters over his 17 seasons with the Cardinals, winning two Cy Young Awards and a pair of World Series rings in the process. Steve Carlton pitched in the Majors for nearly a quarter-century, winning 351 games and leading the NL in whiffs five times. 

Both Hall of Famers were known for their nasty breaking pitches -- but who had the better slider?

Was it Gibson:

or Carlton:

You decide:

[poptip]