One of the challenges I believe we all face is the question of different or better?
Yes, we hear a difference, but is it better or just different?
Often the answer is obvious. Better or worse.
But when we're challenged to decide between two good product versions, how does one decide which to go for? Perhaps unit A leans a bit towards soft and luscious, while unit B tilts toward clear and precise. Both have their merits. Neither is perfect.
One easy answer is to ask which is more like live instruments or voices. Unfortunately, this is rarely adequate because we don't know how the reference music was recorded. You would want the version that more accurately represents the recorded music, not necessarily the sound of live instruments.
My best advice is to begin broadening one's musical choices. The more tracks you can score the unit's performance on the better chance you'll have of coming up with an accurate assessment.
It's great when it's a no brainer. But for those times when you're scratching your head, quantity of samples usually wins out.