I've always enjoyed tracking the movements of the Voyager spacecraft, largely because they were both launched only a short time before I was born. In a sense, we're triplets! I doubt I'll ever get in far in life as the Voyagers have though, seeing as how they're both many billions of miles away from the Sun by now and I'm no further from the Sun than the day I was born (minor orbital perturbations notwithstanding). If we ever have the technology, I'd love to go visit one of the Voyagers out in interstellar space, just to say hi.
What are your favorite spacecraft?