I think you should try both.
So far I am a cartridge (aka cart) person. I enjoy playing with my flavor. If I have a tobacco ejuice in the cart I might add a bit of vanilla, or chocolate, or add a bit of a sweet RY4 to a darker tobacco. I also mix desserty flavors. if I want more TH I add a drop or two of a higher TH eliquid. I just like playing with it. Even when I am just vaping vanilla, I might add a bit of chocolate or fruit or just a different vanilla just to change it up.
I can mess with my cart and juices at work at my desk, at home, and my ride to work is short. I don't have a pressing need for a cart that lasts longer. But some people do have longer rides, or jobs where they can't mess with carts and juice, or just have a desire to have one flavor in a carto that will last longer.
Another factor - I was a lights smoker and I am not looking for a big hit. Some cartos actually put out more vapor and more intense flavor than I need. I would just be wasting juice if I used cartos, and possibly upping my nicotine dependency.
re the dud empty cart that comes on an atty - I use that after blowing out the primer from the atty then priming it with juice and vaping that off without inhaling. And one of my PVs has manual batteries that still have a hole in the end and an external atty bridge so when I dip (rather than drip) I use the dud empty cart to vape.