That's a tough one, it's probably Molgera, but Kalle Demos is close too. Trust me it's coincidence that they're both the ones that can eat you.

I really like Molgera's fight theme but also the sand physics is cool and also I found the way the smaller sandworms arc backwards when you jump slash kill them to be really satisfying.

Kalle Demos is very pretty, and also the way it eats you in it's bulb is hot