Several members have posted positive comments about Mercury and Dolphin, even to the point of claiming them as their favorite browser. I haven't used either, so that's pretty much the limit of my opinion. If they are working for you, with all the options you want or need, and you like them, then there really is no need to get Atomic as well. It's a nice clean UI with good features, but from what I hear so are Mercury and Dolphin.
I only mentioned Atomic and iCab because they are what I use when I need more than Safari. I've had them both for a long time (as iPad history goes), before Mercury or Dolphin were available. They do what I want, so I haven't been exploring the newcomers.