I'm not sure how the Fonseca winery compares to others but it we loved our visit there. The property is gorgeous and they give you an audio-tour so that you can walk around the vineyard and hear about port history and grape growing. After that, a free tasting. It was great. Fonseca is west of Pinhao, along the road from Regua.
This is indeed a tough question, however I think visiting any of the following would be worthwhile as they all produce fantastic wines:
Quinta do Vallado
Quinta do Crasto
Niepoort Vinhos S.A.
Quinta do Mosteirô
There are also others such as Quinta da Leda (Sogrape) and Callabriga (Sogrape) that are worth visiting too.
For helpful hints and more info on Portuguese wines see these excellent sites:
Please let me know if I can help or answer any questions.
Vinhotinto 75, many thanks. Could I trouble you for two more questions? (1) we would prefer to use public transport in moving from Porto to the winery: does this change your response? (2) might you have a good website/link regarding agritourism-type hotels in Douro and/or the north of Portugal? Thank you in advance for any thoughts you may share.
Using public transport to get to most of these places is usually not the best option as they tend to be rather remote. There are tons of different organized (non-touristic) tours by boat and car that are worth seeking out to visit some of the finest estates.
Still - there are some public transport options for visiting the Douro (See below):
Likewise, you could go to Peso da Régua (Régua) which would make a fine base for visiting wineries and doing local gastronomic tourism as it is known as the center of the Douro. The city's website has links to info about the area as well as information on lodging and such:
The following site is the official site for Pousadas de Portugal which are historic inns and guesthouses throughout the country.
The Rota do Vinho do Porto website has tons of useful information regarding the many different estates, producers, and lodging. The page with the map contains tons of links:
Lastly, if you decide to stay in Régua or another town along the Douro, you can take the Inter-Regional train from Porto to Régua (about two hours). The cost is something around 7 Euros each way.
Here is a schedule in English and Portguese:
If you come here to Portugal in November, it is fall wine and chestnut season!
Please feel free to let me know if I can help in any way!
We just returned from a trip to Portugal that included several days in the Douro, and though it is not an agritourism-type hotel, I highly recommend Casa do Visconde de Chanceleiros. It's a manor house in a beautiful location in the center of the region, and it was one of the highlights of our trip.