I use the plastic Wilton bags, couplers, and tips as they are most available and least expensive. I have a few PME tips that I love, as they do not have a seam. I've never used a syringe, as I was taught using bags. I would think that using a syringe would not give me as much control as a bag? (probably just what you are used to!)
I like to use icing plugs when doing a lot of piping with an assortment of colors or when icing cookies. There are a lot of references to icing plugs here, but to quickly summarize: Place one cup (more or less is fine) icing on some plastic wrap and wrap it up like a long fat sausage. Twist both ends shut. Just snip off one end of the plug and drop it into a piping bag when ready to use it. The plugs store easily, allow me to refill bags quickly, and keep my bags cleaner.