Do you like Apples? Or do you like Oranges? What you're asking is a personal preference and how you use your BB. Personally, My 8300 sits in a box on the shelf and never turned on. I use my 8820 everyday. I leverage wireless pretty much everywhere I go. Does that make it a better phone/PDA/e-mail device? For me... yes. For you? Who knows? The 8820, 8300, 8310 & 8320 are ALL excellent devices. It's just a matter of what fit's your needs best.
There's not really a wrong choice here.