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In practice the quality of an eyepiece is easy to determine based on how clearly it shows dim stars at the magnitude limit of the telescope. That's basically what happened last year and it was a good test. Find the dimmest possible star with eyepiece X - if Y finds a dimmer one or pulls in X more easily, it is almost certainly a better eyepiece in an objective sense. For some eyepiece pairs it will be no contest - for others a lot of X/Y back and forth will be needed. In any case it's a completely objective criterion and only needs a good high contrast scope and dark skies to test.

The complication is individual observer's eyes, so I would think you would make up a magnitude chart of a densely packed field down to 14th magnitude or so and let each observer find his own test objects, e.g. in the region of Orion's sword and belt. You also have there B33 as an arbiter of contrast.

-drl

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Very good point that's hard to argue against - if one ep shows fainter stars than another, all other things being equal, it is a better ocular. If one shows stars not as faint but has other advantages such as huge AFOV then that can offset seeing less faint stars. For me, though, this would be my criterion of choice. It also implies superior sharpness because one ep could hardly show fainter stars than another unless it had superior sharpness (and likely better contrast as well).

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