IES is generally more directional lighting. It's good for lamps on walls, or maybe one of those kitchens that have lights under the cupboards. There's never usually a ton of use for these outside of one-offs, imo. I personally use ghost lights to illuminate the environment itself, for the most part, and then use spotlights to light/highlight the figure. They come with the bonus of being invisible (outside of very select cases.), which makes them great for roof lighting, or like the above, just popping them under a lamp shade. They're going to usually be far more flexible than IES profiles.
There's people who do light entire scenes with ghost lights, figures included, but I find the lack of control on them (and the inability to see through them via Aux Viewport) makes them tough to use for that.
All things said and done, being completely equal, most styles of lighting are going to render at about the same speeds. From a pure speed standpoint, though, ghost lights are usually going to win it. I posted these elsewhere for another topic about faster rendering, but feel like it applies here. Everything thing is the same except for the type of light. Angle, size, and everything else are as close to possible as equal.