For critical hits, the PHB states:
When you score a critical hit, you get to roll extra dice for the attack's damage...
The description of acid splash states:
... A target must succeed on a Dexterity saving throw...
The description of the Unconscious condition says (leaving out the first 2 bullet points):
- The creatures automatically fails Strength and Dexterity saving throws.
- Attack rolls against the creature have advantage.
- Any attack that hits the creature is a critical hit if the attacker is within 5 feet of the creature.
So a sorcerer sneaks up to a sleeping creature (within 5 feet) with the intention of doing as much damage as possible, and can either fire bolt it or acid splash it.
Fire bolt — The advantage of being unconscious is negated by the disadvantage of making a ranged spell attack at 5 feet. If it hits, the damage is rolled as a critical hit.
Acid splash — The advantage of being unconscious is now obsolete because the target automatically fails Dexterity-based saving throws. The spell automatically hits as a critical hit.
Does the acid splash spell work this way?