Stop your search! This is your place to stay in Porto. I use Airbnb all the time for work and pleasure and can speak from experience when I say it doesn't get any better than this. There are three main reasons why:
1) The location is exactly right. Minutes away from all the places you want to see, but still quiet and charming
2) The place is modern, sharp and gorgeous. Lots of light and a great use of space. And of course, the garden out back is a stunning, private oasis in the middle of the city.
3) The host - Daniel went absolutely above and beyond to make us feel at home. He was an excellent host and made it is his personal mission to see to us being looked after and taken care of. It really was extraordinary.
I can't recommend this place enough. Stop your search - book this place.