My goal here is mostly to read articles, but sometimes I save the website for archive purposes. Which one do you think I should choose?(Sorry for my bad English I am not a native speaker)
I don't use it and inthibibthere might be some privacy concerns but I think Firefox bought pocket. It's useful for just this purpose. You bookmark (pocket) a webpage for later reading and it syncs it to your devices in a readable format.
However, to more directly answer your question, it will completely depend on your use csse. Either should work but pdf will be more reliable.