Check out the GB Porn thread for more info.
On current models, as the preamp section is now the same between the Rumour and the spitfire, the only real tonal differences are down to the woods you choose! The pick up placements are fairly similar as well.
The main difference is the feel. The body shapes balance very differently, and the only way to decide which is 'best' is to try both and see which suits you the most.
The Rumour tends to be the most highly thought of, I however can't get on with the shape, and so went with the Spitfire, which I the most comfy and well balanced 'Jazz' style body I've ever had my hands on.
Shep