The authors mention the mantis shrimp in the first sentence. So, presumably, the ant is faster.

>CHAMPAIGN, Ill. -- Move over, trap-jaw ants and mantis shrimp: There's a faster appendage in town. According to a new study, the Dracula ant, Mystrium camillae, can snap its mandibles at speeds of up to 90 meters per second (more than 200 mph), making it the fastest animal movement on record.

From the paper at https://royalsocietypublishing.org/doi/10.1098/rsos.181447 it is 90 m/s vs mantis shrimp's 30 m/s.

> The duration of the snap movement is one thousand times shorter than the snap of a human finger and five thousand times shorter than the blink of an eye

Compared to other ants:

> The power-amplified mandible strikes of other trap-jaw ants, such as the genera Odontomachus and Myrmoteras, take three to sixty times longer than the snaps of Mystrium

And further:

> Snap-jaw ant mandibles exceed the velocities and accelerations of other arthropod power-amplified movements, including trap-jaw spider chelicerae (8.5 m s−1, 103 × g) [34], mantis shrimp dactyls (30 m s−1, 104 × g) [35], and froghopper jumps (4.7 m s−1, 102 × g) [36], and have 10–75 times the power density of these movements.

First line of the article is "Move over, trap-jaw ants and mantis shrimp". From wikipedia[0], the mantis shrimp claws move at 51mph vs the ant mandibles of over 200mph.

[0] https://en.wikipedia.org/wiki/Mantis_shrimp