Located 620 light years away from Earth, Kepler 22b is probably the likeliest candidate for a habitable exoplanet. It is located in the habitable zone of its Sun, the only "Super Earth" discovered to have this characteristic as of yet.
This gives it the rather nice quality that its average surface temperature, of 74F, similar to that of Hawaii (hotter than Earth's average temperature).
Terraforming it would therefore be easy, perhaps even unnecessary. All it would consist of is ensuring a proper atmosphere of oxygen and nitrogen as well as the presence of water. Along with the addition of life.
Kepler 22b has 1.45% Earth's gravity, an acceptable ammount. A person weighting 100 pounds (yes they're light) will weigh 145 pounds. An uncomfortable, but adjustable change. If the planet is not habitable for human life, it can be easily terraformed.
In an unlikely scenario: If Kepler 22b is already inhabited, ethical issues would stir up. If the life is microbial or primitive, nature reserves can be built. If sapient life is found, we can form reservations or attempt to make diplomatic contact