I agree with everyone else that the round is better on the stovetop...
I have a 6.75 qt oval Le Creuset, and when I brown meats before braising, it only heats in the center, and not on the two long ends of the oval, which sit on the outside of my glass burner. Might be useful if I wanted to push the done pieces to the ends, and continue browning in the middle, but not really.
I think I use mine for braises, mostly with smaller chunks of meat, and not whole pieces, like your leg of lamb. As such, I think a round would have been better suited to my needs. I'd consider what you cook more often - whole pieces meat, or small chunks. Whole = oval; chunks = round. I wish someone said that to me before I bought my oval!
I also have a pumpkin shaped Staub that I love. I'd consider the performance and the quality of the two to be equal. Another thing to keep in mind is that the interior of the LC is blond, and the Staub is black. It's easier to see caramelization of the fond in the LC.
I have a few more LC pieces, but I do love the whimsy of the Staub. Cute cover handles on some, and funny shapes, like my pumpkin smileys/smile.gif
The cover handles on the Staub are usually metal, whereas the handles on the LC are a poly-something, so its limited to something like 450 degrees in the oven, if that matters to you.