*** This is one issue where perspective will give different results: handling and pulling all of them apart on a regular basis, I'd say that (These are my personal conclusions, not a challenge to anyone or any brand... for my own layouts, I tend to build my own loco's anyway

):
* All are quite OK in the main - and represent their prototypes in accuracy and detail well enough for general credibility.
* "electromechanically" there is little to choose in the mid market position at all. all 3 prototype areas you mentioned have well detailed reasonably accurate models available.
Some brands have more sophisticated motors but overall gearbox/motor/wheel relationships are good.
Generally some EU models certainly look to be overpriced on a pragmatic level but market reaction/demand allows it so who is to say its overpriced really.... it will probably not change.
* Main compromises as I see them:
1/ EU still has unnecessarily large flanges - big flanges do not have any positive effect on roadholding so I think its a carry over habit - some brands are now using some quite nice wheel profiles on some models, but this remains an EU weakness compared to the quite nice current UK wheel profile and the nice but still a little coarse RP25 used on most US prototype. (RP25-88 would be nicer)
2/ Only US has a reasonably prototypical coupler which is well and consistently applied to a good set of standards.
3/ Only EU has a really consistent approach to smoothly operating automatically adjusting close coupling (but otherwise, the couplers are still pretty naff look wise)
4/ Lighting wise UK models are pretty weak, US much, much better technically and EU not bad technically and often very good visually but still mostly wired for "train set auto reversing" rather than prototype operation.
5/ Inadequate cross brand compatibility couplers in UK prototype, better in EU, totally OK in US prototype.
6/ Weakness for traction tyre use in EU prototypes, some cross infection of this nasty feature into UK, very little for US (and where fitted, spare non-tyred drivers always supplied)
7/ I may be wrong here
but to me there is far too much use of self coloured plastic on EU models, especially in the area of the red wheel/underframes. Now almost none in quality UK stuff, almost never any now in US prototypes of quality.
Overall, I'd not be influenced by any of the above for choice of prototype to model, but I'd take them into account when choosing the brands I bought.
Richard