I usually have an initial pick based on visuals, then i maybe change my mind if someone else catches my attention when i see videos of them, who has the best vibes, who do i find most relatable and so. For me the biases often shift over time so in most groups i don't have a constant one ÷)
I usually learn all the names and then start watching variety content and seeing who stands out to me in mv's! I tend to pick the one who's personality I enjoy the most or admire in a field (main dancer, main vocalist) etc :>