It probably depends on your vehicle, the traffic, the specific roads, and many other factors.
For me, attempting to Pulse & Glide on the highway in my VW is terrible for my fuel economy. Because it is so low-geared, 70mph is 3000 rpm; and because I'm not very good at rev-matching, it's wasteful for me to get in and out of gear at that speed. I have been doing what I call "Pulse & DFCO" but I'm not confident that it's the best choice. For my current tank I'm trying just setting the cruise control and so far, subjectively speaking based on the gas gauge position, I think it's better.
In my truck P&G is reasonably easy on the highway but it doesn't coast long so it probably doesn't help much.
Others on this board believe that constant throttle is better than constant speed, though I don't know the theory behind that idea.