I had a 15ga angled Duo Fast double sequential that I liked. It was in the Great Robbery and so I need another one. They are a must.
I didn't use it for stain grade finish work because the holes are too big for stain grade. Some WWers don't mind stained putty over 15ga holes but I think it looks like a dog's butt. I used it for carcass construction and hanging cabinetry, interior door hanging, and some paint grade trim etc.
The 16ga is also too big for most stain grade apps IMO but alot of finish carpenters use it anyway.
Since you have an 18ga, I would go with an angled 15ga. An 18 and a 15 will cover alot more applications than a 18 and a 16.
Of course at some point you'll see that you need a 23 ga pin nailer, 21, 19, 18, 16ga brad nailers, the 15 you are getting, and a few assorted staplers as well. Oh and did I mention a palm nailer? They are essential when you need one.
