My personal favourite Gigantamax is Kingler! I love his bubble beardstache and his spiky spider legs! The design would have been perfect for a Mega Kingler with the ability Water Bubble.
Gigantamax Kingler was a nice surprise for me actually, Krabby and Kingler I feel don’t get a whole lot of love. The stache and the beard are high tier goofery and I it a lot, it’s a fun play with the whole crab/bubble thing you see in Japanese media (it might extend outside of Japan too at this point but crabs spittin’ bubbles is a thing I’ve noticed primarily in Japanese stuff)