Okay, I'm not a photographer, so my opinion is probably not worth much, but of the first 3, I like #3 the best. She has a slight tilt to her head and it gives her a softer expression. Between #2 and #3 was hard because they are so very similar.
And of the last two pics, I like the first one best for the lighting (pic#4), and because she has her head tipped slightly forward, giving more length to her muzzle. Her eyes seem like they have a bit more expression in pic #4 also, and her tongue is cleaner, lol. I can't believe I noticed that, but I did :
She is just too adorable - such a soft expression. I personally like head shots with the mouth closed if possible but out of these I like the last one - I like the closer up views and the last one I think probably shows off her true color because it was taken without a flash. Out of the top ones I like the first one - she's looking directly at the camera.
Of the first 3, I like #3 the best. The face is the lightest and you can see the expression and catch lights in her eyes.
Of the last 2, I like #4 the best. The lighting is better on the face. The mottling on her face is wonderful.