For me:
1. Haruna. For a long time, Scandal was ALL Haruna for me. She's still by far the coolest, sexiest, and (in my own opinion) the most charismatic of them all. I'm in my 30's so part of it may be that she's a little older, although only by a couple years... but in Japan, that makes a big difference in how you're treated by others so it can make a big difference in how a person acts. She comes across as really strong. Sometimes you just look at someone and say "she's a rock star", and that's always how I've felt about her. I also think she's a better guitarist than she lets on. I think she's probably as good as Mami, but her role is vocals and rhythm guitar so that's what she does. Oh, did I mention that I love her voice?
2. I guess Tomomi, although Rina's close. I used to think Tomomi was a little too much sometimes, but she's grown on me lately, and I actually think she's the best musician of all of them. She is a really good bassist; she could play in any band. When I read that she was an RHCP fan, I respected her even more
3. Rina. I usually think she's the cutest of all of them, and after seeing them at Budokan, now I know she's a really good drummer too!
4. Mami. I like Mami but I feel like she usually takes kind of a back seat to the others. Her personality actually comes out more in their behind the scenes videos on the DVD's that come with the CD's than it does in the PV's or live videos.