I really like KZ iems, but lately I think I'd be better with fiio, e ne though I haven't bought any. Are they really better or is it just the brand name?

That depends on what you want. Most KZ IEMs are rather v shaped. What do you want to improve? There's nothing wrong with being fine with what you have and the best IEM in the world isn't necessarily of much use if it doesn't suit your taste.