You could break down the requirements of a character to be "played well" and see results with, then rank characters accordingly.
I think one of the best indicators of a difficult to use character would be option coverage; a character who has fewer decisions to make will be a simpler and easier character on a decision making level, whereas a character who has specific tools for specific situations and must constantly choose those appropriate responses would be more difficult.
Example: you have a move that hits on both sides of you and lasts awhile. This move makes it so you don't have to worry about the spacing on things like crossups, or worry as much about the timing on covering options like dodges. Using this move well is not difficult and gives good rewards, so in this instance, difficulty is low. If a character could always rely on this move and win games, winning with that character would--as a result--be simpler than winning with a character lacking such a move. When a character has options that lack downsides, decision making becomes much easier and therefore playing the character well becomes easier.
Tech-floor is another. Tech-ceiling obviously means your character's maximum, but what does your character demand of you to even be able to compete at all? Yoshi would probably have one of the highest tech-floors in the game, since he mostly lacks mixup and spacing options without excellent DJC control and his shield game is terrible without implementing his parry. At a lower level Peach has virtually no tech-floor, but at a higher one she can be quite demanding. Same with Marth. Let's be honest about Fox; how technical do you REALLY have to be in order to see excellent results? Not necessarily perfectly optimal results in every scenario, but to yield good returns off correct decisions? Not as high as you might think, for his tournament worthy basics.
Window-size; kind of like option coverage but more specific. Your option for winning a scenario may exist, but then it may also require excellent timing. Again, your character would--in this situation--demand good response choice and execute that response with precision. Falcon's d-air -> knee is easy to execute once you land the d-air because the window for hitting with the knee is usually so large (from both spacing and timing perspectives). So in that scenario, Falcon is an easy character.
Of course, then it bears asking how well Falcon's d-air covers options, and how hard it is to land a d-air in the appropriate percent window on a grounded opponent. These would have to factor into the scenario so you know how easy it REALLY is to do a d-air -> knee.
Risk; do your viable options involve lots of risk? Wobbling is easy, but against a competent Fox with IC experience, any opening can yield a dead Nana and suddenly you are not quite as good a character, so there are times where going for a grab is insanely risky. And how easy is it for the Ice Climbers to grab a Fox, and in what scenarios can the grab occur? Taking these into account will give you more insight into how difficult or easy it is to execute a character's options.
Payoff: characters with lower payoff require more good decision making. Simple.
If your character has nothing but high risk options with small window sizes that only work in specific scenarios and require years of practice to execute, then I think we would say your character is pretty difficult; you need good timing, execution, and decision making, and screwing up will kill you. At the other end, your character might have low risk (difficult to combo or kill yourself with), great range and windows on landing your moves, simple execution requirements for using your viable options, and on top of that it's easy to see which option is best in a scenario. That character would be very easy.
So if you want to judge how difficult a character is, I recommend taking factors like the above into account.
Final note: don't confuse viability with difficulty. When discussing difficulty, we assume a character has the tools to be viable, and then we discuss what the requirements are for using those tools. You don't say a video game is difficult because there's a segment with a wall that you can't pass and so the game can't be finished; you simply say "the game can't be finished," and you're done with it.
![Эикельманн [РУС]](/data/avatars/l/153/153661.jpg?1415225120){kind=avatar}
