One advantage Futaba has over Sanwa is that Futaba designs and makes their own wireless IC's. They have been an industry leader in 2.4 datalink technology for many years, even before they became popular in the RC world. If you open up a Futaba receiver you will see Futaba brand chips. Other brands use different wireless chips. This gives them better control over the hardware and software they use in their radio systems.
In the RC airplane world, the link integrity of Futaba is legendary. Sanwa, Graupner/JR and Spectrum have all had range/integrity issues in recent years.
Futaba also pioneered serial communication servos (Sbus), which have lower latency and even better resolution than PWM servos. You can get JR's serial (Xbus) receivers now and everyone else is working on serial buses now too. It will just be a matter of time before we have nothing but serial radios.
Again, in the airplane world, JR/Spectrum and Sanwa have sponsorship programs, where they pay more travel expenses than Futaba. I would imagine it is the same for their car teams, which is pretty attractive for a pro level driver.
For surface radios all of this is probably less of an issue, but I feel a lot more confident in my Futaba radios than my buddies who have all had problems with other brands.
In reality you probably can't go wrong with any of the current generation radios. The technology is just fabulous. You should go handle all of them and try them out if you can. There might be one radio that just has better ergonomics for you. Just like in practical shooting, the feel of the pistol grip is everything. Some guys just can't shoot a Glock because of the funky grip angle. You might have a similar deal with your surface radio.
Hope that helps.