The most common and most likely answer to this crossword clue is the 6 letter word NICEST
I've seen this crossword clue in The Guardian
N
I
C
E
S
T
More clues leading to the result NICEST
- Insect in a pickle? Most delightful
- Most pleasant scent I sprayed
- Least likely to upset possible clients with no end of mail
- Most agreeable for a city street
- Exotic insect is most particular
- Most agreeable lollies, say, in New Territories
- N Most pleasant time, since at sea
- Sweet things in book collection most delightful
- The Promenade des Anglais, perhaps, is most pleasant
- Nut hollowed out and filled with desserts is extremely sweet
Buddy explains!

The straight part
We know that "Most pleasant" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case most pleasant = nicest.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does NICEST mean?
NICEST adjective- Pleasant, satisfactory.
- Of a person: friendly, attractive.
- Respectable; virtuous.
- (with and) Shows that the given adjective is desirable, or acts as a mild intensifier; pleasantly, quite.
- Silly, ignorant; foolish.
- Particular in one's conduct; scrupulous, painstaking; choosy.
- Particular as regards rules or qualities; strict.
- Showing or requiring great precision or sensitive discernment; subtle.
- Easily injured; delicate; dainty.
- Doubtful, as to the outcome; risky.
- Nicely.