I have noticed with the current boom, Gengar seems to be the fan favourite with a lot of the newer collectors, Whilst in my LGS a few weeks a go the cards that were selling more than other’s were Gengars.
Also a young co-worker (19 year old) has spoken to me about Pokémon recently and expressed interest in getting a PSA graded Gengar because they think it is cool. I don’t use social media but I would guess Gengar is popular on there.