In all 3 pictures I like the eye level perspective and the overall composition. The background for the first pic is a little on the messy side though. You tend to centralise your subject a little too much try keeping your dogs face a little to one side in horzontal format pics but if you want to go for a smack center approach your eyes must REALLY grab attention.
This brings me to the lighting. lighting wise for all 3 its a little too flat for me. #1 is pretty good but the straight top down lighting on #2 and 3 make your dog look a little dull plus they all look a underexposed on my LCD. Remember that your dog has fur covering his eyes so they will tend to cast shadows either add in a fill flash to create some sparkle or position him in such a way to catch the light in is eyes naturally.
Overall pose wise #3 has the most potential. Remember ideally portraits (this is what this thread is about) should not just capture the face or image but the character of the dog. His confident expression along with that bone shows more personality to me that the first 2 shots. If you want more tips you can pick up this months copy of photovideoi (I only browsed though but it looked informative).
