Answer:

rarest

Answer	Crossword Clue
RAREST	Least common
RAREST	Most uncommon
RAREST	Quite scarce

RAREST	Least often seen
RAREST	Most scarce
RAREST	First served?
RAREST	Hardest to find
RAREST	Most desirable, maybe
RAREST	Most unusual
RAREST	Closest to extinction
RAREST	Least well done

RAREST	Closest to unique
RAREST	Found least often
RAREST	Supremely scarce
RAREST	Most sparse
RAREST	Red to the max
RAREST	Least cooked
RAREST	Hardest to come by
RAREST	Most like a collectible

RAREST	Most red
RAREST	Hardest to get hold of
RAREST	Most red in the middle
RAREST	Superlatively scarce
RAREST	Most extraordinary
RAREST	Most elusive
RAREST	Most interesting to a numismatist
RAREST	Least prevalent

RAREST	Seen least often
RAREST	Least likely to be located
RAREST	Most prized by collectors
RAREST	Toughest to find
RAREST	Descriptor of the 1867 one-cent Z Grill stamp
RAREST	Hardest to locate
RAREST	Most infrequent
RAREST	Most hard-to-find

RAREST	Least likely
RAREST	Most limited
RAREST	Least available
RAREST	Least seen
RAREST	Least often encountered