Beware: Do not confuse adjectives and adverbs.
2-syllable adverbs ending in -y form their superlative with the words the most.
Of all the people I know my father drives the most quickly (quickliest).
Other adjectives with two syllables:
Other 2-syllable adjectives: use the most with the unchanged adjective
The most boring thing about ESL class is doing grammar exercises.
My sister is the most careful person I know.
Exceptions
The superlative of some shorter 2-syllable adjectives can be formed with -est.
- simple - simplest
- clever - cleverest
- narrow - narrowest
To be sure which comparative method to use, you will need to consult a good dictionary.