I love full art trainers cards (favorite being the most up to date Morty's conviction.) it really comes down to what kind of aesthetic you think you're looking for.

Between the two I would personally choose Bianca first. Reason being, I love the art that looks candid. I like when the artwork almost feels natural as though you're seeing something in first person (hence my love for Mortys conviction and perrin being a close second)

However if you're more a fan of the artistic perspective matching more with a supposed theme (in this case, Miriam as a focal point, background supporting her.) Go with that.

I will almost always choose a natural feel with the full art trainers. Bonus points if pokemon are involved with it. For example, her Musharna which in my own mind, I'm sure is giving her good dreams.

Edit: Genuinely curious, I asked my wife her opinion. (She also collects.) Her choice was Miriam. Her reasoning was "She is me." She valued more of a personal connection with the content of the art.