Which one is the best choice...Ipad or Nook?

I like reading e-books.Currently I read them on my cell phone.So,I've benn considering getting a Nook to make my life easier.But lately I found Ipada the perfect choice for me because I don't have a laptop and I supposed I will have 2 gadgets in one purchase if you what I mean and e-reader and an "computer".So I believe that my purchase will worth it If I buy and Ipad rather than Nook.Tell me your pros and cons of both devices,and which one should I buy? Thanks in advance