Why I think Amy rocks? Why people love this character?
Is it because she has a big hammer she uses that somehow fits her like a glove? eh, maybe, it feels more of her design
Is it cuz she has a cute design? heck no (the best part is the hammer)
Her personality.
She has a very rich personality, and of all the Sonic characters, she's been through the most noticeable character development over the games.
She's very lovable and sometimes relatable, she has a lot of depth to her personality-wise, in some ways a lot of other Sonic characters don't show.
That's why Amy's a great character