Jillian is so country to me. I know Jillians and Jills that are totally plaid shirt and pigtails kind of girls. o_O Or at least they were when we all went to middle school and whatnot together.
Julia is a beautiful name, so pretty and classy and regal. It strikes me as a sophisticated choice in as of itself, but certainly it is in comparison to what I think is an "elaborate but missing the mark of elegance" Juliana.
As a matter of interest the only Julias I know are between 50 and 70; every one of them goes by Julie.