Which one to get???

Hi everyone!!!

After being in here for a while and seeing everyone talk about how great their ereaders are I think I am ready to buy one for myself!

However, I am unsure of which one to pick, the x3 or x4? I like to read all sorts of things, including manga, and would ideally like something that would be able to fit in my pocket. I believe the x4 screen is close to 4 inches, and I have an mp3 played of similar size.

Are there any distinct differences or pros and cons between the two?

Thanks!