Ideally a good dancer with a nice enough personality.
But if I had to choose out of your choice, a good dancer without a personality (presuming you mean the personality of a person rather than the personality they exude through their dancing).
I've enjoyed seeing wonderful pro dancers (of whatever dance disciplines) that have horrid personalities and yet I can tolerate not liking a person if their dancing still captivates me. I've had dance teachers and fellow pupils that were highly talented and could still inspire me despite not liking them as individuals off the dance floor. In my own experience, lots of the best dancers have the most difficult personalities off the floor, and yet on stage or in classes and training they exude so much dancing personality that you're still reeled when watching them.
I love dance, simple as, and i'd prefer to see a dancer win. I will always prefer a Ricky Whittle type person to win over a Chris Hollins type person. Of course I appreciate those who try, but if you still can't dance by the end, then it's not going to be a winning candidate for me.
But ideally someone that had a good balance of both, like Kara.