Q12
I've had a Quad 12 for about a year and I think its a very good car. I use it for modified on carpet. For stock class my Speedmerchant car is faster but I like a t bar car for modified and The Q12 is the best (for me) of all the cars I've tried. Good quality graphite and a good design (although a square front would be more durable). The battery retention system works well (I modified it a little) and of course is quicker in use since it doesn't require tape.
I can't compare the Q12 to the L4 since I've never had the latter but I don't think you will be dissappointed if you try the Q12.
O'D