I think you have to keep Rondo because we have a shot at the title this season.
In a vacuum I think Griffin has a higher ceiling, big men just have a bigger impact. So I'd do the trade if the C's were at a rebuilding stage.
In a vacuum, out of a vacuum, current situation, rebuilding situation, I take Rondo. Griffin had season ending surgery to repair a broken Kneecap. I recall a big guy named Oden (ironically, also a number #1 pick)who had surgery to repair a broken kneecap also. Ask the Blazers how that one worked out.
Rondo, even given his aggressive nature has had nothing like Griffin's injury. Little nicks here and there, but nothing close to career threatening. He's pretty durable, relatively speaking.
For that reason, alone, I like Rondo. People mention ceiling. When Rondo's jumpshot is completely established, he could be a franchise player, a HOF, perennial all-star and sometimes MVP candidate. His ceiling is as high if not higher than Griffin. I can't see Griffin a whole lot better than he is now (Which is pretty darn good, I will agree.)