I could be quite happy with any number of options, as long as the options chosen are used to fully take advantage of the benefits of doing it that way. For example:
Traditional D&D method--yes, rename spell "levels" to something else, like "circle", and emphasize that it is not directly tied to character levels equally--i.e. a wizard progresses in arcane circles faster than bards, etc. And really use this for finer gradations, that work--i.e. the bard stays some fixed amount behind instead of getting further and further behind merely to keep a regular pattern.
Or Keep spell level equal to character level in a system that has 20 or 30 character levels, but unlike 4E, do not have the spells or "powers" occur at fixed intervals. The advantage of such a system is that you can have things like "fireball" be a 5th level spell, while traditional "3rd level" spells that were slightly weaker or more powerful than fireball can be a bit higher or lower. That is, a caster might have a "5th level slot," which he can fill with any spell 5th level or lower, but particular casters might have mainly 4th or 3rd level spells to put in it, because that is what is available to them. In other words, having 4E style with "powers" only occurring at fixed intervals kills the main reason for having 30 levels of spells in the first place.
Alternately, keep the traditional cantrip through 9 divisions, rename them levels 1-10, and have each character class only go to 10 levels to match. Now it takes a lot of play to gain a character level. Advantage here would be to have some relatively narrow classes and do some interesting things with multiclassing so that most characters eventually dabble at least a little with another class or two. Getting to 10th level in a class is pretty amazing. Might need some scaled stuff with skills, feats, and the like to occur inside levels, to keep it interesting. If so, people would have the option to grow more organically within a level, or take it all in one big lump (and keep the character the same for long periods of play). Naturally, that would appeal to certain playstyles.
I'd be quite happy with any of those, because at least they are internally consistent and predictable.