Top-notch rock band in seaside attraction (7)
I believe the answer is:
premier
'top-notch' is the definition.
(both can mean excellent)
'rock band in seaside attraction' is the wordplay.
'rock band' becomes 'rem' (REM are a US rock band).
'in' is an insertion indicator.
'seaside attraction' becomes 'pier' (I've seen this before).
'rem' put within 'pier' is 'PREMIER'.
(Other definitions for premier that I've seen before include "First (minister)" , "Leading" , "Earliest" , "Foremost" , "First in rank or degree" .)