I don't see any of the three choices above as ever rising to legendary status, unless Mexican fans want to consider Alberto Del Rio for the honor in a nationalistic sense; he certainly has the family connections to qualify.
Dolph Ziggler as legend?.....never
Not Daniel Bryan, either. No, I'm not trying to insult the little guy or outrage the good folks on this forum who are fans of his, but while he has enjoyed a brief cult following based on a "Joe Everyman" persona and a catchy chant, what we're talking about here is legendary status....i.e., all-time greatness, immortality & all that good shit.
Can you see him in the same category as guys like Bruno, Flair, Hogan, & Sting? If you can, we're too far apart in definition of what a "legend" is to come to an agreement on this topic.
To me, John Cena wouldn't be a legend yet because he's still performing....presumably a long way from retirement....and it must be recognized a lot of things can happen between now and the end of his career.
However, if he isn't a legend already, he'll be the next one, imo. That's my answer to the question asked in this topic.
There's no one else I see at this time, although back when Rock and Austin were performing and we wondered who the next big thing might possibly be, who knew John Cena was sitting in West Newbury, Mass, waiting to take the mantle?
That's the problem with legends; they're sneaky little devils. They don't show themselves until we've become convinced they're not out there.