Rock/Cena was a huge promotion, maybe the biggest of all time. Worldwide. It was the most successful, one match attraction pro wrestling program in history. Not only from the business aspect but from every source, the locker room to the fanbase were all emotionally invested in everything and on every word. The match was a great, memorable match and the program, ignoring all the hypocritical BS in the content, had classic moments and great performances overall.
However, John Cena is not Hulk Hogan. Which is why it was impossible from the start. The Rock vs Hulk Hogan is arguably the greatest match of all time because it was the two biggest stars ever in wrestling and in the mainstream media to the random viewer. Along with that they're the two best crowd workers of all time. It was such a rare and special moment to see them in the ring because of this reason, it was a monster force vs a monster force. In Rock/Cena, Cena always looked inferior no matter what they tried to do with him. It was out of his league.
Rock/Hogan is the most memorable moment of all time along with a 5* spectacle match. You can't beat that until you can find two new guys who are at their level, and that means that Rock and Hogan are going to be 3 and 4 which is just not going to happen because you're never going to see this kind of talent, star power and charisma ever in the business.
Rock/Cena, like Jericho said, is the Rock/Hogan of this generation, it was special, unique and one of the greatest programs of all time with the perfect match payoff, but you can't duplicate the magic, lightning and thunder of Rock vs Hogan.
Rock/Hogan - *****
Rock/Cena - ****1/2
In terms of a buyrate, Rock/Hogan did the bigger domestic number obviously, Rock/Cena takes it in every other category. Although that's unfair to compare because it's different times and standards. Both broke the record for the most successful event in pro wrestling history, Rock/Hogan in 2002, Rock/Cena in 2012. That's what really counts.
The Rock/Cena feud entered a territory that only a few were able to, Top 10 of all time. But Rock/Hogan was legit "Who will go down in history as the absolute greatest ever".