Guys I would put above him:
Deron
CP3
Rose
Guys I would put on his level:
Nash (better offense, worse defense)
Westbrook
Wall
Wall and Westbrook are not on Rondo's level, they could be, and maybe they could be better, but right now Rondo is a better PG.
Rose is very good, a great player, but he's not a better PG. Rose is a better scorer, stronger player, but he doesn't defend or create for others like Rondo. And I know I'm biased, because I love Rondo's game and dislike the way Rose plays, but they're on a similar level.
From my perspective, there's no cookie-cutter definition for "point guard". Sure, Rondo is a better passer than a lot of other guys. However, he also doesn't score like some other guys do. In determining offensive impact, you have to look at both of those things, as well as efficiency, range, etc. There's more to being a point guard on the offensive end than just making great passes.
As for defense, I think Rondo's has slacked off a bit this year (although it's still very good), while Rose and Westbrook are being underrated on that end. Rondo is still the best defender of the three, but the gap isn't a huge one.
I checked their production vs opponents production on 82games counting net possessions as the added differences of shots + .44*FTA + turnovers + rebounds. If you use more possessions than your opponent you lose possessions, using less means gaining possessions.
Paul gains you 3 points and and .5 posessions and 4 assists
Williams gains 6 points and 4 assists and loses 5 possessions
Rose gains 14 points and 2 assists and loses 12 possessions
Westbrook gains 10 points and 2 assists and loses 9 possessions
Rondo loses 5 points and gains 7 possessions and adds 8 assists
This isn't the only way to judge point guards, but it's meant to demonstrate than Rondo's other contributions raise his impact to their level. It really does depend on what you're looking for and how much you value scoring over passing and defending.