Whenever I am in Porto, and I go often, I stay at the Residencial Rex. Jose is an excellent host, always willing to assist with any need. The entire staff goes above and beyond. The Central district is a straight shot - I've walked it in 15 minutes - with plenty of good restaraunts in evey price range nearby. The accommodations are not elegant and there is no internet access, but it is quaint, clean, comfortable, and affordable.