If you are going to crop a group of shots that are going to be displayed together then it would look better if they were all in the same format. Pick the biggest one and crop the rest to that size.
BUT they are great fireworks shots especially for the first try.
You have some pretty good shots. A suggestion, when you shoot them next time set your camera vertical. You will catch the tails going up as well as the burst and no dead space to crop out.
I agree with everyone, those are pretty dang good for a first attempt! My first attempt is a bunch of smoke, I had absolutely no luck. You did great, congrats!