Me too I've had the NTC3 and the MTX3 and trying to tell you an unbiased comment of the two is almost impossible but will struggle to do.
As sbmon said, NTC3 is the champ in unprepared surfaces, their sealed gearboxes is definitive here, the shaft transmission dictates a very compact and simple transmission that excels into a very low drag tranny, this means more power transferred into the ground. This is a handicap too, specially on low traction tracks the lack of belt strenght says for a very responsive throttle and probably a very pretty wheelspin with the lose in traction and control.
This low drag transmission dictates you in a different driving stile, to reach the same speed in a turn, you may need to release earlier the throttle and make the inertia of the transmission do the rest, sometimes, the disk is abused by this, but the brake pads are real fine to do this task, sometimes I've seen a colored and warped brake disk (really abused), but is a secondary problem (Hey AE, think on a vented disk... changed 3 disks in less than a year).
Car sometimes is fragile and prone to break and/or change their setup if you slam the boards, this is specially true if you fit the Graphite conversion (IMHO: The worst cancer you can fit in your car).
The stock setup was less than usable, at least for me and neeeded to rework the stock setup and have my own baseline for the setups (very true on the 'foam setup'). Was a car that gave some headaches and many hours of thinkering to get a good performing car.
Other places to revise from the car is the stock clutch... the stock clutch springs are the first one you need to change it to have a better clutch. The car lacks of anti roll bars and front one-way (needed if you plan to run foams). Servo saver spring was needed to be changed for a stiffer one (don't know if this has been revised in later running changes of the car).
The fuel tank, gave some headaches in the past (thrust me, had the old and 'dreaded' tank and didn't had any problems with it), other that shocks people is the funky exhaust pipe, and forces you to use the LD3, the RD Logics or the AE pipe, so pipe selection is somewhat limited.
The MTX3 was a very pleasant experience to assemble, all the part fit without problems, weren't any parts that needed a deburr (well, the shock pistons needed some filing, but this was all the parts that needed a filing or deburring), the manual isn't for a novice, the lack of explanations is compensated by the quality of the drawings.
The stock setup of the MTX3 is about at 90% of the ideal setup on all the tracks I've been (bravo Mugen for this). Only minor tweaks to adapt it to personal likings. Adapting to different track conditions doesn't means to have a miryad of parts like springs, oils, different rollbars, etc... In fact, the stock springs are the best performing ones in all around, in fact, Mugen released a little stiffer springs than the stock to permit better tunning.
Durability: The alloy used on plastic parts is very stiff (not brittle) and durable. In fact after a full season and more than a year (14 months) of racing with this car: this is all the parts I've broke so far in this car:
- Rear bulkheads (broke a nipple that supports the rear shock tower).
- Front upright.
- Rear A-arm.
- Front belt (only one), the rest of belts have been changed as a precaution lately, with more than 50 litres of fuel drawn by the tank.
Adjustability: Is a very tunable car, responsive with the changes you do it... in fact, you can do a change and determine in a lap or two if you did it well. In fact... when I tune mine car all what I do is a pair of laps and see if it improves and pit another time. Very responsible and very adjustable.
Price: Probably isn't one of the cheapest cars, but to be fair, it includes parts that are considered optional in other cars: Centax-like clutch, front adjustable roll bar, rear roll bar...
Hop-ups: Is one of the cars with more hop-ups available on the market. You name it, probably is available from someone. Try to get a pair of MTX3 cars from two different people and see they put different parts on their cars. Isn't a matter of correcting defective parts, is somewhat like tunning. But in between this miryad of parts, very few are interesting to put (this has been discussed a lot of times on the MTX3 thread, just fall by and ask for). But on their stock incarnation is a very serious performer that doesn't need hop-ups. Each MTX3 owner put what he wanted to their cars, but in the base, remains being one of the fastest and easiest cars to drive and adjust.
Is a 'mature' car. This isn't bad... shows how fine was made and engineered. In fact, along the NTC3 is one of the 'oldest' cars in the market that is competitive on the track (V1r has the Evolution model and almost everyone switched to Evo). Mugen will not launch one car each 6 to 9 months and ask you for a complete change of car (like others do...).
Probably you can still asking but many people who drives an MTX3, drove an NTC3 in the past and many will tell you the same, all two are fine cars, but the Mugen (and others.... just check FastHarry
) convinced to many many many people who decided to leave running the NTC3 for the MTX3 or the R40 or the... <nameityouhere>.