These are really good! The contrast, color, and sharpness are outstanding! My only crits would be (just my opinion):
#2, It would be nice to see the dog's face or more of the dog's body.
#3, Too much black space. I would crop it down to give more attention to the details of the flower.
#1 and #4 are so nice! The colors just pop, especially in #4.
Great job, keep up the good work.
NJ