Ok, here's the scoop on both kits.
I have the Fairlady kit, and my friend has the A.M.
The Fairlady comes with stock tires, a booster 57 mhz. chasis, a 2.2 engine, and a Fairlady body.
My friend's A.M. came with four bodies (Blue RX-7, Yellow Supra, Red R34, and a black R32) a 27 mhz. booster chasis, stock tires, and a 2.2 engine.
They're pretty much the same cars, except the Auto Modellista kit's controller doesn't look as cool as the Fairlady's, but it does have a longer antenna wire so you may get a tad more range with that one (my friend and I can't really notice a difference).
Another good thing about the Fairlady is that you can race (and own btw) American made ZipZaps and other clones. I would highly advise you to get some things from TinyRC to go along with your new purchase. I would advise a R-Spec or 3.0 motor, a tire kit, a gear kit, and a stabilizer kit (that comes with a drift axle).
I hope this kind of helps you make a decision,
Yaksha