I prefer disposable..
"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.