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I agree with Bratislav, except with these caveats:
If your scope is undriven and you are pushing it to follow a planet that drifts from side to side across the field, then definitely a coma corrector like the TeleVue Paracorr is called for. Otherwise, the image will be unsharp outside of a very small area in the center.
IF, on the other hand, you add a tracking platform and you now can hold the planets dead center, then, for planets, you don't need a coma corrector and just about any decent eyepiece will show you all the scope can see in the seeing conditions under which you're observing. Seeing is the greatest factor in determining the quality of the image, not the eyepiece. There is no magic eyepiece that suddenly makes seeing better.
For wider, extended, objects, then merely having tracking is not enough, and the coma corrector becomes more important again. We have all read innumerable accounts how such and such an eyepiece is "terrible in my dob", but "the images clean right up when a coma corrector is added". Well, duh. Of course they do--you just eliminated the coma from the mirror and, in the case of a Paracorr, also flattened the field slightly.
The primary difference you'd see between the top tier eyepieces like the Delos, and a lower-tiered one like the Hyperion, is at the edge of the field. Being free from induced astigmatism, the star images in the outer 50% of the field will be a lot better looking with the Delos. Will that matter for planets held in the center? Not really. Will it matter when you are letting the planet drift across the field? Yes. But we still get back to the coma corrector once again.
Where would I put my money if I were a hardcore planetary and lunar viewer?
1) tracking platform.
2) coma corrector
3) THEN maybe a better eyepiece, though it is hard to beat the lowly Plossl for planetary images.
so, maybe:
4) Gasoline. To drive me and my scope to sites where the seeing is better.
We have a few sites around here that are that much better than average. Everyone, with every eyepiece in every scope remarks that the images are better at those sites. Just points out how important seeing is.
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