I would have to say it’s hard to pick a number 1 member so it’s easier for me to pick a #1 in the groups. And as of now it’s:
Morning Musume: Reina
Berryz Koubou: Momoko
°C-ute: Nakajima Saki
S/mileage: Dawa

But my favorite H!P member of all time will always be Aika.

And as for group it’s MoMusu but I was a fan when BK, C-ute, and S/mileage were all formed so I can’t say they all don’t hold a special place in my heart.