Im slightly biased....... another vote for MX5
Here is mine at Castle Combe
And with the missus driving
Yes its slow, but the handling is great in these cars and they are just so much fun to chuck into corners with very little regard for the speed and whether it will exit the corner In all seriousness, its a great car on track, usually the slowest thing out there, but wow can it play catch up in the corners! Mel managed to overtake an MR2 at Castle Combe exiting Quarry
We visit Castle Combe (a little scary considering lack of run-off in places), but still a love track and Thruxton quite often (pop in if you are in the neighborhood). In fact we are at Thruxton tomorrow with the MX5 and the GTR. MX5 has only got coilovers, seats, harnesses, rear half cage, some minor brakes bits and wheels/tyres done. Still testing the suspension, pictures were road settings so still a fair bit of roll, but have some new settings to test for tomorrow which should get her cornering flat.
I enjoy driving the MX5 on track just as much as the GTR... GTR is great for the fast aspect and the MX5 is great for learning the track, RWD and to just have a bit of fun on track.
EDIT
Thruxton is £190 for the day open pit lane, fridays are usual empty and good fun
Castle Combe is £190 for the day open pit lan, but can get busy