Hnnngh, I've had both before, and they're both sweethearts. Ava is more like the mother hen, while Alice has a writer/quiet personality, to me anyway. I voted for Alice, however, because I like her house layout better.
I've got Alice right now, nice girl. Hasn't requested any PWPs since she moved in though. Probably not fair since I haven't given her much of a chance. I've got three koalas right now and they're pretty cool cats, no wait... I'd go with Alice though that's without ever meeting Ava.