An Amazon, just because they're awesome!
In all seriousness though, I wouldn't recommend a certain type of bird. I'd ask them to think about a few things such as available space in their house (for cages, play stands, etc.), their living arrangements and neighbor situation to decide on the volume of bird (a macaw or cockatoo just wouldn't work in an apartment!), and their bird experience to determine what size of bird they're most comfortable with. Something like a yellow-naped Amazon isn't a great first bird!
After that I'd give them some suggestions of species that might work for them and tell them to do a lot of research on them and to handle as many of those birds as possible. Also they should keep in mind the life span of the bird they are considering. Don't know where you're going to be in 20 years? Don't get a larger bird that has a 20-50 year life span. If you're younger, have a steady lifestyle but know you're not going to have children or anything for 5-10 years and don't have a plan after that, maybe a budgie is right for you.