I voted for Alissa. Her positions are incredibly steady and not contrived. Her centering and speed are first rate. Especially the way she accelerates on her sit spins is amazing. I also like her biellman the best. She may not have butt-to-head flexibility, but I find her position the most aesthetically pleasing and comfortable.
Out of the current ladies I like Yukari's spins the most. Alissa and Caroline are also great. Mao has amazing spins in practices, unfortunately she gets much slower in competitions (not enough stamina to do all that difficult stuff, I guess).
all time - Lucinda Ruh ("good for you, Lucinda Ruh!" )
current - Alissa