I have both an iPhone 4 and a 3G iPad. I use both on a daily basis.
My iPhone has basically been my personal assistant since the first one in 2007. It has all my contacts, mail, and apps that make my life easier. It also keeps me in touch with what's happening in the world with apps. Mine is integrated with Google Voice and is vital to my communication.
The iPad is my consumption device. When I want to read an article, watch Hulu Plus or Netflix, the iPad is what I pick up. I also have it jailbroken to run MyWi as I travel a lot and refuse to pay for crappy wifi at hotels. The 3G (I'm lucky enough to have kept my unlimited data plan) is a real life saver for me. I originally bought the wifi only version but returned it and waited for the 3G model.
I would seriously think about waiting until after CES in January to see if Verizon will or will not get the iPhone.