As always, the new dudes goal, budjet , and expectation based upon previous referance (genere & compared to what previous experience), should be the important criteria here; Rather than which has the best "Referance potential" based upon others budjet and goals in defence of "which is best, with multi caveats"...IMO...
For instance, the HD-650s(my second 'phones), were very disappointing in my first system of Headfive / Squeezebox / lossless files / Bluejeans I/Cs / see sig. for generes (ie. better recordings/ masters/mix... Whereas the k-701s, to my ear in that system smashed the HD-650 into little tiny bits to be found in the k-701s stool, to borrow the phrases above.
Entry level systems, expectations and budjets(sub $1200 systems, perhaps), IMO&E & if I were you, knowing what I know now, well you get the idea, see sig
You mention an A/B test... Of course, that's the best test, in your systems and to your ear, rather than others goals, budjet, systems, and referance as to which and what Headphone is "The Best"...
BTW, the Senns HD-650 is the "Best Headphone" potentially, of the two, for many.
Good luck~