Any of the three kits you mentioned can win and be competetive
providing you do your part. To this list you could also add the
X-Ray 808, Mugen Mbx-6 and Jammin X-2. All are good kits.

It all comes down to parts support and driving style as to what
one is going to suit your needs best. Personally I would never
own a car that I had to send back to the old country for parts
so without local support the X-ray and Mugen are out of the
question for me. We have racers using all of them in our state
Pro Series and any of them can hold there own so long as the
driver holds up there end of things.

Of the three you mentioned I will give my observations.

Kyosho Mp-9
Ultra low mass and drag drivetrain requires more maintenance
than other cars but the rewards are worth it. Great shocks and
overall high quality of parts. Conventional drivetrain and weight
balance makes for a somewhat aggresive car. Likes to turn in
hard and be rotated through corners.

Losi 2.0
Offset drivetrain makes for a slightly more forgiving car to drive
fast. It wont turn in or rotate as well as others but is far more
stable and fast coming off corners. Very popular car here in
the States so there is an large amount of setup data avalible
for just about any track. Very tough plastics.

Ae Rc8b
Heavy, but bullet proof drivetrain. Conventional drivetrain layout
favors an aggressive style like the Kyosho. Nothing turns inside
an Rc8b, of course you pay for that with a car that requires a firm
hand to exit corners with any speed. Much improved car over the
original, that car was not bad once you took care of a few details.
The new Bs are just a much better car out of the box. Like the
Losi they are popular and setup data is plentiful.

I would recommend you stay with whatever car is most popular
at your local tracks. Spare parts and knowledge can be very helpful
somtimes so it makes sense to run with the crowd.