Quite a few of these are really good sprites, especially the Tauros with Machamp (?) tickled my fancy, but you shouldn't just limit yourself to the same type of fusion over and over. An idea, even a good one, gets old really quick so you have to adapt, come up with new stuff, be ambitious and creative... that's your duty as an artist. You could probably create hundreds and hundreds more of these centaur things (especially since you also use trainer sprites, which I'll admit is pretty cool) but after like 5 or 10 we've seen it.
So what I'd do, if I were you, is select the best out of these (definitely put the Tauros/Machamp in there, or I'll kill you) to showcase and get general C&C on, but at the same time try something new. As I said, it's your responsibility to decide exactly what you want to do but if I see you making anymore centaurs by the time I give this thread another look I'm sure that'll be the last one. Don't take this personal, you have some potential but it's time to start doing other stuff. It's the same with those spriters who stick to recoloring, they lack ambition to try and go for something more challenging.
As for your actual spriting work, I'm glad to see you made almost no technical mistakes on your best ones: you position your parts (albeit Copy/Paste, but that's acceptable) well, you recolor well and you seem to have some imagination (like on that Mewtwo/Seviper I really like what you did to the eye, really good), but it's time to put those skills to better use. Since there's no chronology in your sprites I don't know if these are your older ones, but some of them DO have problems. Mainly problems where you copied parts and flipped/rotated them without changing the shading (Charizard/Milotic e.g.) but since your better works don't have those problems, I'll just 'assume' that the ones who do are your oldest.
Also, in response to your comment on my work I'd like to say that, while I do feel flattered, I prefer constructive posts with a bit of meat to them (to quote Frozen_Voltorb). You may want to read up on the sticky here ("Concerning C&C and general posting"), it'll help you understand. Thanks and keep the spriting up!