Oberon, as seen by Voyager 2
Oberon is Uranus' second largest moon and it's second most massive. It is scarred with meteor impact craters, and a system of chasmata. It consists of nearly equal amounts of rock and ice, the ice being in the mantle. A major problem concerning the terraformation of the planet would be that the moon has to endure 42 years of light at one pole, and another 42 years of complete darkness at the other; this would mean somehow changing it's orbit around Uranus to prevent the atmosphere from freezing over on one side. The same would be said about Titania.
Terraforming Process[]
First we would artificially heat the moon, creating a weak atmosphere of water vapor, nitrogen, methane, and ammonia by melting suface ices. To heat the planet further, SF6 would be added to be make up around 0.1% of the atmosphere. As the surface water-ice begins to melt into a global ocean, electrolysis of the water could form most of the Oxygen, and Nitrogen can be made by bacteria which convert ammonia into nitrogenous compounds, to make it more Earth-like. Greenhouse gases alone wouldn't be enough to stabilize the temperature to Earth-like levels, so a hydrogen-fusion heat ring similar to Triton's could be built. Finally, a strong magnetic field generator would be constructed to keep Oberon safe from solar storms which may strip its atmosphere (being outside Uranus' magnetic field).
See also: Oberon Simulation