I prefer disposable..
the nice thing about the parchment triangles, is when you just need a tiny bit of icing for glue or small accents you can cut the triangle in half and you have small parchment bags.
"CK Products parchment triangles 15"
I've have had the box for ages, don't remember where they came from, but I use them often.
I love featherweight bags, and don't mind disposable.
I don't like that with disposable, if your using a thick icing the bag can burst from the pressure.
So I put the icing in a disposable bag and cut off the end (a fair bit, maybe 2 to 3 cm), prepare the featherweight bag with a coupler and tip, then put the disposable bag (that's full of your icing) in the featherweight bag. Then you only have to clean a small amount of the featherweight bag and the tip and can throw the other bag out.