[Eclipse]

Yes it's stock, and rooted. Although What are the pros of changing the rom?

Touch wiz is gay for pretty much everything but the note series. A custom rom gives you an experience that's simply unattainable with stock.

Cons: You'll need a custom recovery which will trip the knox flag and void your warranty. Updates are more frequent but nightly updates can be buggy.

Cyanogenmod is my favourite rom.

[Oni]

Yes it's stock, and rooted. Although What are the pros of changing the rom?

All sorts of things. You're changing the operating system. Stock ROMs also contain a lot of bloat (i.e. carrier apps).

[Eclipse]

All sorts of things. You're changing the operating system.

Technically you have the same OS but a different variant.

Stock ROMs also contain a lot of bloat (i.e. carrier apps).

This. Fucking this. The best thing about root is the satisfaction of getting rid of those useless fucking pieces of shit that're taking up space.