Pretty simple question, really.
I used to build radio controlled kit cars (mostly Tamiya 1/10 scale) and pretty much invariably, whether buggies, trucks, or road vehicles, they used double wishbones at the front and either a solid rear axle for 2WD models or a double wishbone setup at the back for 4WD models.
Why not MacPherson struts, trailing arms, torsion bars, or whatever?
I don’t know why they use double wishbones in RC cars, but I know why they do it on real cars.
There are several double wishbone set-up variations, but basically, it is the only suspension configuration in which wheel angles (camber especially) do not change with suspension travel. This greatly improves handling.
The drawbacks are increased complexity (and of course cost) and that it requires more space, which makes it especially difficult to incorporate d-wishbones into modern front-engined, front-wheel-driven cars. So, in most cases, McPherson is preffered (cheaper, requires less space). But most expensive sports cars and supercars (and some Honda Civics )have double wishbones all around.
The rear solid axle (also called “live” axle) has the disadvantage that it makes car handling a little tricky. But on the other hand, it is cheaper and sturdier than independent suspension. All heavy vehicles (tractors, big pick-ups) have live rear axles. There is no way independent suspention could cope with that weight.
Also, live axles have a big advantage in off-roading, because they offer better wheel articulation. For example, when one wheel is depressed, the axle forces the other wheel to extend. You can see this in this pic: http://members.lycos.nl/Bowy/images/terreinrijden/ermelo05-03/axle-twister.jpg If the car had independent suspention, the rear right wheel would be in the air.
Usually they put independent suspention on the front to improve steering and handling, but some serious off-roading cars have a live axle at the front as well.
Not a very popular thread
Anyway, I wanted to add that double wishbones have another disadvantage; limited suspension travel. Not an issue on a track, but it is quite important on public roads.
Correct me if I’m talking out my ass but I thought I had seen off road RC cars that used something closer to a swing axle front end. That is a lower wishbone only with the spindle rigidly attached to it and a coil over shock to support the load. Kind of the opposite of McPhereson where the spindle it attached to the strut body.
I used to mess around with the Tamiya cars eons ago. I had the frog which was a pretty popular model. Although it was 2wd, it had rear independent suspension via a trailing swingarm. The gearbox was in the middle, so the axle was split in half. Each half had a universal joint in it that would move when the swing arm swung.
Here’s a picture, where if you look hard enough you can see what I’m talking about.