The YZ250G/H is a highlight. Nearly as easy to get along with as a trailbike, but still goes like a proper MXer.
The YZ125E is a really sweet bike that just happens to fall on the wrong side of the pre-78 cut-off. If the class structure suited them better, then they'd be everywhere - virtually unbreakable, sweet handling (heaps better than a D), easy to get along with, and generally one of those "balanced" bikes that isn't amazing in any one aspect, but does everything well.
But if it came down to it, I'd always pick my YZ125X as my favourite. My D is faster, has a better power delivery, handles better, and fits me better - but the X behaves in a way that just makes sense to my brain, so I can get around an MX track faster on it.
It just makes sense (to me) so it can be ridden to the meagre limits of my ability without wasting time thinking about what the bike is going to do.