It's best, I see, to be in a home (6)
I believe the answer is:
nicest
'it's best' is the definition.
(I've seen this before)
'i see to be in a home' is the wordplay.
'see' becomes 'c' (the word for the letter, according to Chambers).
'to be in' indicates putting letters inside.
'a home' becomes 'nest' (I've seen this before).
'i'+'c'='ic'
'ic' going inside 'nest' is 'NICEST'.
(Other definitions for nicest that I've seen before include "most appetising" , "Most agreeable" , "Best" , "Most attractive" , "Most appealing" .)