Question

which one has maximum % of enol content

Answer 1

The methyl group in acetone does stabilize the carbon-carbon double bond in the enol form for the reasons you suggest. However the methyl group also stabilizes the carbonyl double bond in the keto form ( this is why a carbonyl in a ketone is slightly stronger than a carbonyl in an aldehyde). In fact, in simple carbonyl compounds, the methyl group stabilizes the carbonyl double bond a bit more than it stabilizes the enolic carbon-carbon double bond. As a result, simple aldehydes generally have a higher enol content than simple ketones.

Hence, the enol content in acetaldehyde is greater than the enol content in acetone.

carbonyl↽−−⇀enolcarbonyl↽−−⇀enol

Keq=[enol][carbonyl]Keq=[enol][carbonyl]

compoundacetaldehydeacetoneKeq6×10−75×10−9