I can't give a short answer, so I will split a few into categories.
All time #1: BoA.
I really liked her
"Copy&Paste" and
"Hurricane Venus" concepts. Plus her lightstick is beautiful! And can we talk about her upside down walk for "Woman". Just in case you forgot how to spell LEGEND:
Current #1: Chungha
She caught my attention with "Gotta Go" so I'm a bit late. I started to stan because of her cute but savage personality. Also her facial expressions when she dances cannot be matched.
Underrated #1: Gyeongree
I really liked her solo performance and hope she continues with solo projects. Hyomin was a close second since I really liked Mango, but some of her songs are hit-or-miss for me.
Overall, Im super hapy Solo artists are making a comeback! I got into kpop via solo artists!