But don't declare Opportunity a champion too soon. The Lunokhod distance measurement was based upon wheel rotations and a map of Lunokhod's progress made with relatively low-resolution images. And any off-world rover driver worth her salt will tell you that wheel slippage and other factors make it very difficult to estimate how wheel rotations translate into actual distance traveled. And any space mapper will tell you that it can be terribly hard to determine the correspondence between craters and hills seen from the ground and seen from space.
Now that we have actual photos of hardware and wheel tracks from Lunar Reconnaissance Orbiter, Russian scientists are re-mapping the Lunokhod traverses and finding quite different numbers, about 42 kilometers in the case of Lunokhod 2! Opportunity has a long way to drive to beat that record. And while Opportunity could theoretically achieve 42 kilometers, now that she's reached the rim of Endeavour she doesn't need to cover such long distances anymore. She may well get to the magic number 42, but she's not in any hurry to do so.
NASA / GSFC / ASU / Sergei Gerasimenko / Sasha Basilevsky
The final resting place of Lunokhod 2
Lunokhod 2 roved 42 kilometers across the Moon over five lunar days (Earth months) in 1973. This image, taken by Lunar Reconnaissance Orbiter's high-resolution camera, shows the final resting place of Lunokod 2, as well as the crater that caused its death.