The graphic associated with this post seems to be more appropriate for "what's the fastest car in the world?"
Regarding the "rarest" part: there's a very well-documented answer, and it happens to be an American made muscle/pony car from the late 1960s. See "world's rarest muscle car."
You can't count cars still in production, as the could continue to make more, however, it doesn't really matter since "one of one" is as rare as you can get.
The crown of rarest production car in the world, which still survives today, belongs to the only 1967 Shelby GT 500 Convertible.
Extensive information on this particular car can be found at 1967ShelbyConvertible.com
If this question were rephrased to the be which car is the most expensive sold at auction, there are plenty of auction and private sale statistics that points toward various vintage Ferrari GTOs.
Previous answer by Grace Anderson: Bugatti Royale Kellner Coupe this is one of the rarest and expensive care in the world.
phantom corsair .... only one was ever made
The Maserati MC12 is the rarest super car. Only 50 have ever been made in the 2 years of production hence the name MC12 a
The rarest element in the world is Astatine.
The VW Super Beetle is one of the rarest
what is the rarest wood in the world?
The rarest object in the world is enriched uranium.
The rarest bakugan is viper Helios
The Glen of Imaal is the rarest.
The world's rarest human eye color is green.
the conus Gloriamaris or glory of the sea is the rarest shell in the world
The rarest fruit on earth in the "Monkey Fruit".