The number (or even the presence of) levels isn't really relevant, imho. What matters to me is how much a character's capabilities change and grow over time.
I also prefer systems that allow a character to improve noticeably at a steady pace. If progress slows down to much, I eventually get bored with the character.
Since you usually have to put some limit to a character's mastery in a given area to prevent challenges from becoming trivial, many systems allow a character to grow in 'breadth' instead, e.g. by picking up additional classes, careers, disciplines, professions, or whatever they're called in the system.
It's also a matter of the setting and the kind of stories you want to tell. Gritty, realistic settings call for different caps than epic high fantasy settings.
So, I really enjoy all kinds of different systems and play at all 'level ranges'.