I'm 65% Fluttershy, 15% Twilight Sparkle, 10% Rarity, and 10% Rainbow Dash. I've put quite some thought into this. ^^" (Wish I could say that I'm 20% Rainbow Dash, but alas, I'm not.)
Fluttershy: I'm really shy around everypony but the ponies I'm closest to, and can relate to often being too quiet to be heard. (That's happened to me way too many times. ^^) If it's between pretending to engage in conversation with ponies and hanging out with their cat/dog, well, I'll most likely be petting that thing for hours. Like Fluttershy, I'm afraid of anything dangerous, scary, or otherwise daunting, and usually don't speak up.
Twilight Sparkle: I'm book-smart and have Twilight's vocabulary, and am usually the voice of reason (that is unfortunately too quiet for anypony to perceive). If you were to ask anypony I know, they would probably say I'm both Fluttershy and Twilight.
My 20% Rarity-RD is the side of me that not many see; the Fluttershy majority usually overwhelms the Rainbow, and the Twilight sometimes dilutes the Rarity. I'm a filly of many sides. ^^"
Rarity: I really try to look my best at all times, and love it when my hair cooperates or my outfit is perfectly coordinated. I can definitely relate to being the creative and artistic type, randomly getting ideas out of nowhere, and especially trying to please everypony's relentless demands. I wouldn't say I'm wildly generous, but I do like making things for ponies. ^-^ I also hate getting dirty.
Rainbow Dash: There's a small part of me, possibly just teenager-ness, that doesn't care what anypony thinks and says "screw it all." I sometimes feel like I want to show off a bit, but I usually don't. And if I do, it's too quietly for anypony to notice. xD
Turned out longer than I was planning... sorry...