We had apartment 4, which sits at the top of a four storey building bang in the centre of Porto Old Town, equidistant to the ribeira (waterfront) and train station (a tourist attraction in itself). Couldn't asked to be in a better location.
The apartment is comfortable and decently enough equipped (modern hob, fridge and freezer, comfortable bed and sofa) but the wow factor in the apartment is the view in three directions (including a long window running the length of the kitchen looking towards the river). There can't be many other rooms in Porto which can offer this, and certainly not at the price.
We will definitely be recommending to anyone we know, and also recommend paying the extra to get room 4 (I think it is unique in the views it offers, although obviously the location will be the same for the others!)