I like them both...the only way they can be compared is because they're sisters. Other than that they're nothing alike.
I've always liked 'Irresistable' and 'Where you are' by Jessica and her voice is amazing. (Shame about her supreme-DUMBNESS. 'Name all five continents'...'a..e...i...o..u' lmao. O_o)
Ashlee's voice is nice, and her song 'Pieces of Me' really rawks and I can sort of...associate with it because I myself have finally found something real to rest my head on and BOY do I like the way it feels.
Lol!