R.U.B.E is great. It is a huge time saver for the creation of box2D levels. The data importer works quite nicely with Cocos2d-x and is fairly flexible. You can create your levels as one file, or separate them into multiple files and import them together. For example, you could design each individual level as a separate scene, and reusable characters in another file and import them together.
You mostly work in the editor using keyboard commands, which once you get familiar with them it is a very fast process to manipulate your objects. There is some very nice documentation built-in along with multiple videos. The creator of R.U.B.E really hasn’t taken any shortcuts there.
The editor also supports custom scripts, so you can automate certain tasks you find yourself doing. Additionally, the data format allows custom properties, so essentially providing the needed custom hooks into your own code for anything you can’t design in the editor (for example, some game logic specific to your game).
The creator is also very active and responsive to answering questions and generally helping out in his forums.
That being said, I don’t have much experience with any other editors, nor have I gotten too far with my own game using R.U.B.E yet, but I’ve not experienced anything negative from R.U.B.E yet and am quite impressed. I would recommend it. It is very reasonably priced as well and supports all the major OSes, so if you are on linux it is especially nice.