Nook Color vs IPod Touch vs Ipad?

I'm trying to decide whether to get a Ipod Touch, Ipad, or a Nook Color. I want something that I can read books, and comics on as well as listen to my MP3 music. Looking for something that supperts Micro or full sd cards for more memory. Also something that will allow me to read my PDF books I already have. Any suggestions would be appreciated.