Hmmmmm, I think this could go either way!
If you mean, who enjoys the feeling of the work getting better the most, then definitely the creator. Readers don't tend to notice as much when it's gradual, but the creator is absolutely aware of how many things they've worked at and gotten better at, and it's a tremendous feeling to put out a page you're actually happy with, or to be confident in something that you struggled with last chapter.
If you mean, who enjoys seeing the evolution from beginning art to improved art, I would say the readers. Readers tend to find it really fascinating and cool, whereas creators tend to want to cry when they look back at older pages. Many comic creators fret a lot over consistency -- seeing their work change and grow is encouraging, but also tends to bring a lot of wistfulness about what the work would be like if the whole thing could've been at their current level. Meanwhile the readers on here have talked a lot about how cool it is to watch a series grow artistically.