We have a VERY good driver at our local track who has run all three cars. He went from the Serpent>Mugen>Kyosho. He ran the Mugen most all season right till the Cincy Nat's where he ran the Kyosho. He said the Kyosho had more turn in than the others, but we were on a permant facility prepared for a National event with 175 cars at the event laying down traction vs. our newly sealed and weekly treated local track with 40 cars laying down traction (which is a parking lot during the week).
Some cars have a wide tuning band- I'd say the widest tuning band is on the Mugen. The set-up is very forgiving.
In the end it is personal preference/cost/parts availability. Don't be the only one at your track running brand 'A' when everybody else is running brand 'B' or 'C'. You won't have much comparison for set-up's and parts availability. At most races I run, parts are readily available for all the top three... Mugen, Serpent and Kyosho. Make a list of Pro's and Con's for each brand in your racing area and see who comes out on top.
My desicion is based on personal preference/cost and CUSTOMER SUPPORT
. The factory sponsored Mugen guy's are only a direct phone call away and more than willing to give advice. Props to Mugen- Mike Swauger, Robbie Collins and Ron Calangi for making themselves readily available to the little guys in the sport for advice