Each gives a different spread of bait, and different ways of baiting up.
When seagulls are being a pain, then it has to be spod or Spomb.
If you want free bait close to your hookbait, then PVA string, bag or mesh. Incidentally I tend to cast out plenty of stringers or meshes full of bait, but rarely loads of PVA bags full of bait, however, it is possible to catapult them out.
As for catapult, you can use it for single or multiple baits, or even firing out small PVA bags or meshes as well as groundbait.
Throwing stick, a good way to get single baits out long distance, or multiple baits shorter distances, but if seagulls are about when only firing out say 1-4 boilies, may be worth forgetting.