I own both a Traxxas Stampede vxl and a Typhon 3s both need about the same upgrades to make them better. Stampede shocks pop off caps, Arrma shocks leak.
Stampede will destroy driveshafts on 3s, Arrmas hold up a little better but can still break.
A arms on both are rather Meh.
The brushed electronics that both vehicles come with are not up to the task of powering a 1/10th scale 4wd vehicle, both have issues overheating and should be replaced.
The brushed Traxxas vehicles are at least brushless ready, the Arrma Megas need to be upgraded to the BLX diffs in order to handle more than 2s.
Traxxas tires are rather Meh but it uses 12mm hex which is very common size, Arrma tires are much better although they use 14mm hex not so common but Duratrax makes 12mm hexes for them.
Steering servos are rather mediocre on both.
Traxxas uses rubber sealed bearings, Arrma uses metal shields.
The Arrma is a little easier to work on.
The Stampede is limited to 3660 motor can before chassis modification is necessary, Arrma will accept most 1/8th scale motors, I know the 4274 motors fit.
Traxxas radio is also much better than the Spectrum STX2 radio that comes with the Arrmas, the best place for it is the trash.
Traxxas does have a larger aftermarket but their platform is also much older, 10+ years for Traxxas only 2 years for Arrma.

That being said I would not bother with the brushed versions of either vehicle as you will most likely upgrade to brushless anyway. Not to mention that the brushless Granite costs about the same price as the brushed Stampede.

Just my thoughts and opinions on this.