I run an I -Force from Darkside motorsports and love it. The engineering on it is fantastic.There customer service is great and I have never had a problem with Eric and his crew.I like that it has the battery slots down the middle of the chassis instead of across the rear.Makes transition between left and right corners smoother(In my opinion). With that said, the I-Force car is a bit on the pricy side so I wouldn't recamend it for a beginner or if you're not sure about running the class.
Also, I have not tried any of the other cars so I don't know what to compare it to. I like the looks of the Associated car, but again, I have not done much research on the others that are available.
Just my two cents.