Neither sounds “wrong” to my ear, but if I had to pick one, hmmmm…I think modular things are inherently versatile, but versatile things aren’t inherently modular, so I would go with “versatile and modular” so it gets more specific from first word to second word.
Or consider not using both those words.
Edit: the order of adjectives usually matters when they are different types of adjectives, like “five big brown bears”. You have a number, a size, and a color. That one sounds wrong if you get them out of order. But modular and versatile are the same kind of adjective, so I don’t think there’s really a wrong choice here.
Is it ever stated that the serpent is actually Satan?