Least sloppy (7)
I believe the answer is:
neatest
'least sloppy' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for neatest that I've seen before include "Seat ten (anag)" , "best-looking desk, say?" , "Most tidy" , "Most smart" , "Most orderly" .)