GT12. They are the right size for an indoor club hall (which I am assuming from your post is your weekly 'fix') and are cheap to buy and run. The class has evolved quickly in the last three years, and has now reached a plateau with three new cars unlikely to be changed too soon.
Due to low weight and simple suspension construction, the cars are light on batteries and motors so they last a long time. My GT12 gear is now on year three with no signs of diminishing speed. Tyres are cheap and last a long time, and set-ups are well established.
Driving foam tyres is usually regarded as easy, but in fact is quite difficult. Lots of TC drivers come into 12th for the winter and all of them will say it has improved their driving skills. Keeping the car within the available grip and hitting the apex consistently for five minutes (the only fast way round a track with a foam-tyred car) are skills everyone who races GT12/LMP12/GT10 has to learn. There aren't any kerbs to ride if you get it wrong!
Top choice would have to be the Schumacher GT12 in S1-chassis-with-differential guise. It's £100 and will be competitive right out of the box. Use the low-grip set-up from the instructions and you'll be on the pace immediately. You may need a small servo (Core RC for £35 is favourite) and a 1S compatible speedo (there's a few of the excellent HW v2.1 120A 1S devices on sale here for reasonable money, or again look to the Core RC one) and a 1S battery to power your 13.5 motor.
I've just put myself on the road with a GT for £165 covering a kit, Core RC servo and used LRP SXXv2 (1S) speedo. I've used the motor, battery and receiver from my previous SupaStox. Driving that car last season has done my driving skills the power of good even though I have been racing 12th for over 35 years!
The key is that the car is fast enough to make mistakes, yet reacts in a way your brain can process really well. Any mistakes mean you lose ground to others and have to drive really precisely to catch up again. Not making mistakes and winning races is really rewarding. Your changes to driving style are easily seen on the clock so anything you try (including set-up changes) give you immediate feedback.
TCs are too big for club tracks, they are not in their element, they need too much maintenance and they have to be replaced every season as the latest ones are always faster than the older ones. They are too fast for mere mortals to enjoy indoors and so fast that crashes cost serious money. GT12 is the reverse of all that, so what's not to like?!! HTH
