i have the 8880 myself and it is very very cool: V8, 4 wheel drive and steering, 4 proper different ratio gears
opening tailgate and fully independent suspension on each wheel.
However its not powered and you won't be able to replace the engine with a motor
because the chain between it and the connecting rod to the gear box will just jump or snap.
so if you did power it (I've seen it done) you probably wouldn't be able to run the power through the gearbox.
the 8448 also looks nice. 5 forward gears and one reverse is impressive but only 2 wheel drive and steering.
its in the newer style so flexible rods and funny plates making up all the styling rather than the more lego styled blocks of the 8880.
I prefer the older style but i think the newer also looks cool so it depends what you like really.
Now I've just has a look at the 9398 and boy does it look fun!
with motorized 4 wheel steering and 4 wheel drive with the super long suspension travel it looks like a blast to play with.
But like most of the new Technic sets it has no gears and with an electric motor you don't need that but i think its cool.
so if you want a fun rc car that you can continue playing with for a long time after you've built it get the 9398
But if you're into engineering and you like to see realism and how everything works get either of the other two.
Just depends what style you like between the other two, i'd say that the 8880 really shows the top end of what lego can do,
they had to make unique parts for this set to allow 4 wheels drive, steering and suspension.
But if the old style isn't your thing the 8448 is a worthy alternative
Hope this helps