Richard Baker wrote:
Korob and Sylvia from 'Catspaw' - totally alien creatures from another galaxy trying to understand humans but locking in on the wrong part of the mind instead.
Tholians are second runner up- as finally shown in their full form later, another true alien race made of crystal, very territorial and as mentioned above, punctual.
While there are a lot of aliens throughout the series, I like obviously the ones which are not actors in makeup but creatures so different that you might not even recognize them as sapient beings, they have their own world view and a lot of difficulty dealing with humans
Along those lines, the Kelvans. And I agree with you. The really alien
aliens (especially non-humanoids) are most interesting.