Most qualified
To successfully complete this sentence, we are looking for a degree of comparison. Degrees of comparison can be positive, comparative, or superlative. Note that degrees of comparison are all adjectives. Positives describe only one noun. Comparatives compare only two nouns. And, superlatives will compare three or more nouns. The degrees of comparison (from positive to superlative) for the word "qualified" are qualified, more qualified, and most qualified. Because the sentence says “of ALL the applicants,” it can be assumed that there are more than two. As such, because more than two are being referred to, the correct form is “most qualified.”