1. Boom Racing- ProBuild Wheels, the selectable transfer cases, PHAT axles, Python servos. The have a complete lineup of just incredible products
2. MST- Thier planetary transmission is sweet along with the chassis on the MTX-1 and their constant pursuit of bettering the drift scene
3. Vanquish- Just seems to be a well-rounded company who knows what they're doing and the marketplace they are going after
4. Traxxas
5. Tamiya- They engineer to just to be different it seems, but it also makes the builds fun
6. RedCat- look at the lowriders and some of newer stuff coming out. They have come a long way!
7. Element- They were looking promising for a while and now still riding that wave, but for how long
8. GMade- Very cool products and hope they continue to get better
9. Axial- I just don't know anymore...i think they gave up
10. Carisma- I think they do a lot with a little. They are not out to be the best, just put out stuff no one else is. They found a niche
11. CrossRC/RC4WD
Who puts together the best engineering and part quality/fit and finish. From my experience Boom Racing, but Vanquish and MST have to be up there as well.
Tamiya is at the top of this list. All the stuff that people are doing now were at some point already done by Tamiya. They had scale trucks before scale trucks were a thing, think of the line of semi trucks they have been selling for decades. These things have had self-locking differentials and multi-speed transmissions for a long time. Tamiya had "trail" trucks before "trail" trucks became a thing--CC01 and Bruiser/High-Lift variants. Monster trucks? Clod Buster. Tamiya had crawlers before crawlers were a thing--CR01 variants, released around the same time as the AX-10 (2008).
I just want to be clear, I am not a fan of Tamiya's current product line-up--they are currently leaning so heavily on "versatility" of their chassis kits and also on their retro legacy(that part I don't have a problem with.) They can absolutely design cutting edge stuff as evidenced by their TRF line, but they are so pricey compared to what everyone else offers based on what you get, that I seem to think that Tamiya has a A LOT of overhead (just think of all the LICENSED bodies they produce), and it shows in their offerings. They are not a performance brand currently by any means, but they have the ability and capacity to do it at any time if they wanted.
When I think of "engineering," in the RC world, I think about new ideas or new categories of vehicles that are being brought to the table. You surely can make a high quality product or improve upon an idea, but that's more like adding beats and re-mixing an already great song. So in terms of engineering, based on this list and behind Tamiya, I have:
Axial: expanding scale derived drivetrains and vehicle types to the RC world (solid axle, rock racers, desert racers)
Traxxas: the Slash--full fendered bashing racing machine that had semi-scale appearance and movement; the Summit basically made all the selectable drivetrain features and packaged them into something that was very durable; the Unlimited Desert Racer is still the top dog and the standard to which all desert/go-fast rigs will be judged against--though Axial's Yeti came out first, the UDR refined that concept to something more.
Losi (not on your list): but with the acquisition of multiple brands (through Horizon), they have basically turned things like solid axle monster trucks (the only REAL monster trucks IMO) into performance vehicles that don't break all the time. They produce the only current alternative to the UDR in the Rey series, and they have provided an alternative, more user friendly way to drive/balance RC motorcycles
Runner Up: Redcat has some very original thought in the lowrider series and they have evolved their crawler series year after year. The rest of their lineup is derivative of everything else.
Runner Up: Kyosho (not on your list) but they had the first "scale" motorcycle that actually behaved like a motorcycle in the "hang-on" series; they were a pioneer in the nitro powered 1/8th scale on-road and off-road scene particularly with the Inferno series.
The rest of that list don't really make anything that is original--they make high quality products, but it's all a derivative of something that was already designed, they are just making it out of a "better" possibly more durable material, which does require engineering, but not really as innovative as some of the examples already listed above.