Not sure I could give you an order for Greg and Temps, I like them both. Matt is a bit dull but he does a decent enough job of facilitating. Prutts is by a huge distance my favourite guest.
The format works best when it's Matt / expert / fan, if they don't have one of Prutts / Lewis / Fletch / Birtles then it's just fan stuff. Having an ex-pro / broadcaster balance out the fan view with professional insight is where it's really interesting IMO.