They both enhance teammates abilities, have both won championships and both are likely Hall of Famers.
Deciding who is the better point guard is highly dependent upon the makeup of the team. Also, there is the matter of the age of the team: Rondo is about four years younger than Parker.
Rondo still hasn't hit his prime (scary), and he offers more value to a team that is possibly years away from winning a title.
In terms of their games, Parker is a better scorer, and Rondo is a better facilitator. That's not really a matter of debate. Parker has never averaged more than eight assists per game, and Rajon Rondo has eight on his bad nights.
Rondo has the third-longest streak of 10-plus assists games (34 and counting), while Parker gets a 10-plus assist game once in a while.
But, Tony Parker can shoot. Tony Parker has won a Finals MVP Award. And Tony Parker has three championship rings to Rondo's one.
So, it's not all about just assist production. There are other factors measuring of how much a point guard impacts his team.
The real crux of the matter is how much better a defender Rondo is.
Rondo averaged over two steals per game for his first five seasons in the league, and last year was his first season under two steals per game (1.7). That's not even to mention how many deflections Rondo gets, nor how often he frustrates opposing point guards to the point of tears with his long arms and quick feet. He's a game-changer on both ends of the court. Tony Parker isn't.
Ostensibly, Rondo has a lot of work to do before he can enter Parker's realm of accolades. Namely, Rondo must win more championships and secure some hardware. Parker winning a Finals MVP is no small feat considering he has a standout teammate like Tim Duncan.
Rondo has been mentioned in MVP discussions this year, but for that to happen the Celtics are going to need to be far better than the middling .500-ish team that they are right now. They're going to have to post an elite record—something the Spurs have done for over a decade, dating back to Parker's early years in the league.
What it really all comes down to is this: Rondo is better now, and Rondo can be even better still. But he has a lot to prove before he can pass Tony Parker in conversations discussing all-time greats.
Parker has been in the league since 2001-02, and he's made the All-NBA Second Team (2011-12) and Third Team (2008-09), while Rondo has not yet made an All-NBA squad.
Rondo just doesn't have the body of work yet. But he will.
For all-time career accolades, you have to take Parker. But beyond that, Rondo is the clear choice.