Always best avoiding peak — this the highest! (7)
I believe the answer is:
everest
'avoiding peak this the highest' is the definition.
The definition suggests a singular noun which matches the answer.
'always best' is the wordplay.
'always' becomes 'ever' (synonyms).
'best' becomes 'est' (I can't justify this - if you can you should give a lot more credence to this answer).
'ever'+'est'='EVEREST'
Can you help me to learn more?
(Other definitions for everest that I've seen before include "Himalyan peak" , "Himalayan peak" , "Where Hillary was" , "Mountain on the Nepal-Tibet border" , "A mountain to climb" .)