Hi,
it is not the noise from the DC that makes an NPN a better choise.
With your biasing the output resistance is max 7 Ohms.
There is an other problem.
After this stage the DC restorer followes.
There goes a high current through the 10nF at the sync tips.
So you must make sure that there is a strong source to pull
down!
A NPN emitter follower is a strong source to pull up and
a PNP emitter follower is a strong source to pull down.
This is a very importand aspect.
In your case the 470 Ohms makes the pull down.
So if you have a DC restorer as a load and a negative sync
it is better to take a PNP !!!
The output resistance of the emitter follower should be as low
as possible to make sure that the sync will not be damaged
or gets a level reduce.
You placed a 180 Ohms at the output of the emitter follower
and this will be added to the output resistance.
In front of the DC restorer this is a bad mistake.
It is a DC restorer
not a sync separator!!!
There are a lot of commercial modulators that makes trouble at the top of
the picture because of sync level changes and other mistakes
caused by a wrong driven DC restorer.
I hope I was able to show you that there is a big difference in
the use of a PNP or NPN emitter follower.
In this case the PNP is the better one.
Kind regards
Darius