All the Jetstreams have the same cabin diameter - its the length that differs (and please, try to restrain any smutty comments at this juncture...) the Saab's may be different when it comes to hand luggage (I've not managed to get one of these on a T3 flight). They now only have J41s and Saab 2000s but they did used to have all sorts of Jetstreams and I think some other aircraft.

Another plus is that they always provide copies of the Spectator, and if you get an S class ticket give you lounge access at many of their destinations.

Leather seats, a good read and a glass of fizz... beats many of the others ways of getting round the UK...