I've only read the first Twilight book but all the same I say the Harry Potter books are much better. Bella irritates me with all her 'oh Edward is great, Edward is perfect, I love Edward' stuff. The story was quite good, but I didn't think it was especially well written, it put me in mind of fanfic (and I have actually read better fanfic). I know I wouldn't pay for the rest of the books, but I would read them if they were free, there is something about them which makes them very readable.
Harry Potter on the other hand. Maybe not literary genius, but I love the stories. It really gets you thinking and has hidden depths. Even the characters I don't like have a sort of intriguing quality which makes them interesting if not likeable