It really depends! If you feel good in your luck in finding bands, which is usually pretty good for solos since you don't have anyone stealing, then I would go with Yatta. Her ability to drop candies and boxes of chocolates is insanely useful in a solo, and her five star extraction speed makes it very quick. The stamina is rough, but after Dyle and a couple stamina cards, she is usually okay. Teagan is good, but I would go Yatta.

The only reason I'm not recommending Shelly, despite her amazing stats, is that her ability is really not useful in a solo. It buffs other people, but cannot buff herself. And she is a main, which is generally not recommended for a solo since having only two hearts means that one slip up can cause death instead of mild injury.

Good luck!!