Honestly? Of the Earths we’ve seen, the closest to one that I’d want to see more of as it is would be Earth 5. Every other Earth would need some degree of tweaking before I’d want to see more of it (some more than others).
• Earth 2: there are some elements of the post-Flashpoint Earth 2 that I appreciate; but by and large, I’d rather see it rebooted to more closely resemble the turn-of-the-millenium JSA comics. The ideal for me would be to present it as if the pre-Crisis Earth-2 had survived the Crisis but had subsequently developed in ways that mirrored their post-Crisis counterparts, to the point that the current state of Earth 2 resembles the JSA-related sector of the pre-Flashpoint DCU; but I could see tweaking it somewhat to incorporate some elements of the post-Flashpoint Earth 2, such as Alan Scott’s powers deriving from the Green and Jay Garrick’s speed coming from Mercury.
This is the single most radical alteration that I’d want; it’s severe enough that I could see an argument for assigning a different number to it — though given that it’s more true to the original Earth 2, and that the post-Flashpoint Earth 2 is in the process of being wiped out anyway, I think I’d rather stick to the “rebooted Earth 2” explanation.
• Earth 3: like Earth 2, I’d like to see this Earth rebooted to more closely resemble the Crime Syndicate featured in Morrison’s JLA Earth 2.
• Earth 16: tone down the “media brats” element and include a few more heroes of the Titans and Young Justice generations (e.g., Nightwing, Donna Troy, Tim Drake, Cassandra Cain), and present this more as a “Titans Earth” where the Justice League has died off or retired and their protegés have taken over.
• Earth 4: feature the Charleton heroes, yes; but let the writer establish his own tone and style with them, rather than expecting him to ape the Moore-esque stylings of Pax America.
• Earth 5: I know I said that I’d be fine with it as is; but I’d really like to see it expanded to include other Fawcett Comics superheroes.
• Earth 20: Not enough heroes for my taste; I’d prefer the Society of Superheroes’ roster be bolstered with other Pulp-like heroes.
• Earth 11: reboot it to more closely resemble Elseworlds’ Finest, with Kara Zor-El as the premier Kryptonian instead of “Clarkia Kent” and Barbara Gordon’s Batgirl instead of a gender-flipped Bruce Wayne as this Earth’s “Batman”.