Are you guys talking about one of these?
I would personally rather have that 300 since it's decades newer.
Sure, you might be able to find something that's well maintained, but the metal will still be fatigued and every engineering components will be decades older.
Not saying that Ninja 300 was made with most modern top of the line technology available today, but still...
If that 300 didn't suffer any structural damage, I would personally stick to the 300 since it has EFI, ABS and all.