I don't know from first hand, but I've heard from two separate individuals that worked with both, and both boiled down to the same;
The rabbanut employs experts in their fields, and do a much more thorough check.
One worked in a meat plant, and said that the mashgichim of the rebbanut were far more experts than the badatz mashgichim.
The other one's brother had an orchard; The rabbanut sent an agronom to check it out, while the badatz did not.

Of course I've heard otherwise too...
An uncle of a friend who was sent by the Rabbanut to South America claimed that the Rabbanut's official bodek peered inside a cow he just shechted, and exclaimed... "it's empty! The stomach is empty!" (Rafi, as a shochet, you should know what that means...)

actually, he should either not deign to compare, or should say things like we are better than they are, not we are as good as they are. the former takes the offensive, the latter takes the defensive. of course we are assuming his claims are accurate...

let's face it we live in a world where marketing is king. so the rav has to brand his product. kacha zeh.

Sometimes you just want the truth to be out there. Especially when someone has stated or implied that your work is inferior.

When I was a younger man there were three popular hechserim for chickens. Badatz, Rabbanut M'hadrin, and Rabbanut Yerushalayim M'hadrin. In at least one chicken slaughtering 'plant' the same mashgihim oversaw the exact same processing for all three. Only difference was the bag the chicken went into.

Sometimes it is just about religious politics.

"sometimes" is a major understatement

["sometimes" is a major understatement]

Okay, I was a bit too polite. From what I see, it is largely religious politics.

You definitely don't make claims like that unless you can back them up. One almost-mehadrin hechsher made such pronouncements about 6 months ago, and the mehadrin reps checked them out and came up with a number of leniencies they were using that were not even acceptable in many circles.