I think Skyloft is a fantastic stage. It has a multitude of elements (slopes, pillars, the ledges, nonstandard platforms, varied floor height) that make it a unique arena, each of which acts as a tool that either player can, with creativity, use for endless purposes.
Moreover, these elements are nothing to complain about: they don't really promote camping (besides of course the large size, and possibly the high platform which I've personally had no problem with), and are deterministic and non-intrusive (even stationary and non-damaging) so if someone gets screwed by anything on Skyloft they either deserve it for autopiloting or their opponent earned it through planning/execution. There's a word for people who complain about video games being too hard, and PM should not indulge them.
both parties don't really have much reason to favor it over others in competitive play.
This is really what I think all stages should aspire to, starter or counterpick. Stages should maximize the number and variety of elements they contain (insofar as they are deterministic, non-intrusive, and non-campy) so that the stage is more than just a single gimmick for the chooser to exploit, but is rather a multifaceted work of art that allows deep positional games and requires subtle changes in tactics, so that (ideally) any character could potentially use it against any other. Stages should be balanced around the idea that they're a third character in a match, much like the ruleset itself: a neutral, disinterested party that facilitates Smash's dynamics and doesn't redefine them, and whose effects on outcome are reliant less on the given matchup and more on which player plays it better.
A big part of this is asymmetry, which basically doubles the stage-elements. I really think every stage sans Battlefield and FD and maybe PS2 should be asymmetrical, even if it means re-imagining Melee classics. Honestly, I think the whole roster could use a complete, thoughtful revamp, with no inhibitions against change and no preferential treatment for incumbents.
I think the thought process behind stage choice should consist of more than just looking at a few numbers (size, blastzones, platforms yes/no?) and picking the obvious choice (slow
small, good recovery
far, chain grab
no) which is outright advantageous for your character vs. theirs. The game would be just as deep as and much more balanced than that if we simply declared Battlefied to be the paragon of neutrality and only legal choice, and designed the characters for that paradigm. But we'd be cutting out a major part of what makes Smash so great; instead, stage selection should be a decision of one's preference, and a judgement of the contrary of one's opponent's.
Except for being kinda big (perfect in doubles, though), I think Skyloft epitomizes this philosophy.