What is the best hand-held (PDA, iPhone, Palm Pre, BB Storm) for teachers?

I've been Googling around for awhile and really haven't found a straight answer. I am looking to purchase a handheld device for myself and one of the main things I am looking for is one that can help me manage my clroom - for example, a device with a program where I could check off attendance, participation, write in grades, notes, etc. When you suggest a device, please tell me why and what software on that device has what I need. Thanks in advance!