Some people like Euro collars, but from my point of view, as a harnessmaker (ret) and author of the book, Understanding Harness, they are a complete fraud.
Throat relief would be good, but some of the deep V collars are also poorly designed in an attempt to make breast collars suitable for low draft marathon vehicles, which they'll never accomplish. There is MUCH fashion going on in the driving world to the sacrifice of well researched design. If you're using something like a meadowbrook with a high singletree, some of the deep V collars point down at the ends, and even if the trace buckles are hinged, the fit is crappy. They also have to be tied down in the center with a false martingale, which can be a rub risk. There are some inbetween designs that offer throat relief, lift the collar off the point of shoulder a bit, and have correctly placed neckstrap uptugs, and have a better angle at the ends.
It's a n equipment selection jungle out there.