I say :
1 is nice but a bit too "classic", the background does not help much making it more interesting, and the "cut out nose" is a little "technical" flaw. I know I'm splitting hairs, but you never know how this little things might be judged in a contest...
2 i like this one better, all the diagonal lines fill the composition in a good way and the contrast is good, no evident flaws in my opinion, unless you count the bottom left corner a bit too bright. But fuck that, OR, photoshop it
3 i don't like this, the subject is nice (hello mice) but it has a strange "lab" look, if you understand what I mean...background colours make this a bit too plain for my personal tastes.
4 this is interesting, but the (obviouslyly intentional) lack of focusing is maybe a bit too much for a contest that's supposed to judge pet pictures. btw , I think this last one would look better in full colours (if you turned it BW with some software).
My vote : 2!