Out of those listed I'll get the mini 8ight..
I do have the turnigy buggy, it's good bang for the buck, but quality isn't the best to say the least. Stock setup on 2S is pretty fast and fun, but open gears is a concern if you are going to run on sand.
RC18B2/T2 is alright, protected belt driven drive train and all, but with a little research and you'll find some worrying reviews regarding its' belt being too tight and has a tendancy to rub on the pinion, plus the diff housing and steering crank has a lot of play, if they come up with ways to solve all of these it should be a solid car.
The mini e-revo... well it's just personal preference but I find the body ugly as sin
There's also a new 1/14th buggy coming out mid December called the LC EMB-1, shaft driven 4WD with enclosed drivetrain, don't have a price listed yet though.