well I can comment on the ones that I have owned rather than comment on what I may have read from the "RCTECH national champions" and add another to this list of popular cars.
Agama - handles good but comes with gremlins
Associated - handles not good and like driving a potato chip
Durango - too inconsistent every track needs a new set up. company is confused on what to release 3 years on a prototype?
Hot Bodies - best value, comes hopped up and handles but wears out too fast
JQ - handles ok, feels like a skateboard on the track, some people fast with it, weird things break on this car
Kyosho - the frustrating car, cause its always dialed. a bit brittle and has lost the value of old kyosho stuff. wears out to quick
Losi - handles great, finishes races,always pretty dialed on any track. boring to own if your a wrencher. never change setup and wear could be better
Mugen - they need a 6r.5. the 6r could have had more steering, the 7 could have had more traction. 7 seems weird to drive
SWORKz - another weird one, feels fast on the track but laptimes are slow.
Tekno - will update after I drive mine. best innovation to date. easy to build/work on.
XRAY - xb8 2014 awesome car. handles great and last forever. steering and traction and finishes. when you don't get the famous "backordered" sign its an awesome ride.
SERPENT-only had the 1.0 and it handled awesome but had issues with finishing. all has been fixed but haven't been back to it.