The thumb is generally considered the fastest finger. Research on finger movements has shown that the thumb is capable of achieving the highest speed and movement velocity compared to other fingers.
This finding is supported by multiple studies, including one published in PubMed which found that the index finger attained the fastest cadence and greatest movement velocity, followed by the middle, little, and ring fingers, respectively.
However, it's important to note that finger speed can be influenced by various factors, including individual differences, training, and the specific task being performed.