For several years I taught a course for the Saturday Institute of the Des Moines Public Schools' Talented and Gifted Program on "Astronomy, Space Travel, and Science Fiction." As part of the course each year, the class had to consider evidence from class and from the Internet and decide which of a list of nearby stars they would recommend as the destination of our first interstellar mission in search of intelligent extraterrestrial life.
One year they picked my personal favorite: Tau Ceti, a Class G8-V star in the constellation Cetus which is 20 light-years from us. Our own Sun- a Class G2-V star- would be a fifth- magnitude star in Boötes if viewed from Tau Ceti. In the picture to the right, by R.J. Hall, the Sun is on the left; the somewhat smaller and cooler but generally similar Tau Ceti is on the right.
The system is very dusty and seems to have an extraordinary amount of cometary activity. The latter fact- raising the question of whether repeated mass extinctions might make it difficult for life to develop- is generally regarded as the main argument against Tau Ceti as the abode of advanced life. But it seems that Tau Ceti has at least five planets- and one of them is in the "Goldilocks zone" ("not too hot, not too cold, but just right")- within which liquid water can exist, and in which life as we know it could develop!
It's a great deal closer to Tau Ceti than we are to the Sun. But then, since Tau Ceti is smaller and cooler, that makes sense. If the planet- known as HD 10700e- has managed to avoid being zapped by too many large comets, it becomes the best candidate so far to be the home ET phones.
Sci-fi fans may be familiar with Harry Turtledove's Worldwar series, in which World War II is interrupted by an invasion of Earth by "The Race-" a Reptilian species with a technology far beyond ours. The Allies and the Axis are compelled to drop everything and join forces to fight the common enemy. In the story line, Tau Ceti is the primary of Home, The Race's world of origin.
Another main-sequence star known to have planets is Alpha Centauri, known to Babylon 5 fans as the star around which Londo and Vir's homeworld orbits. It was also was chosen by my kids one year. Another winner was Epsilon Eradani- a Class K star, but still within the range in which life could theoretically develop. It's the supposed primary of Vulcan, Mr. Spock's home planet. Both are considerably closer to us than Tau Ceti- Alpha Centauri is only a little more than four light-years away, and Epsilon Eradani is only nine- and Alpha Centauri is even more similar to our Sun than is Tau Ceti. But neither is known to have a planet in the "Goldilocks zone." And Alpha Centarui is a double star, which complicates everything; while it's not out of the question for a double star system to have planets capable of sustaining life, the complicated orbital and gravitational dynamics would make it a much less likely candidate.
So as of now, if you're sending a letter to ET, you'd probably be best off addressing it to HD 10700ee- that is, if he lives anywhere close enough to our zip code that dropping in for a visit might even theoretically be an option some day.