I don't know how old this thread is, I did a search and found this.
I just installed the eclipse 6620 and love it.
Here is the pros and cons of each.
My brother has a pioneer D3. I think he had to buy a harness to connect the deck.
On the other hand, eclipse (fujistu or something) is pretty much made for toyota. They never changed the deck harness and the harness plugs right into the factory one.
My steering wheel control for the eclipse decks work. No mods needed.
My brothers pioneer d3, the steering wheel functions does not work. You have to buy some kind of module to make it work.
My 2 cents!