We walked from Porto, setting out on 7th January this year along the Coastal route. The first day's route out of Porto sounds the more enjoyable, walking along the Douro rather than walking through residential and industrial areas pretty much back to the airport. There is a fair amount of boardwalk walking on the Coastal (though less than on the Littoral) and not everyone enjoys that. Some people do the first 1/2 days along the Coastal and then cut in from Vila do Conde to join the Central at Rates. I am sure someone who has done both routes will reply to you with more information, or alternatively search the archives, I found a wealth of information when we were planning
One of the reasons some people chose the Central in the winter is to avoid the worst of the Atlantic weather. All I can say was that we were generally quite lucky on that front. It was generally dry, and frequently bright and sunny (by UK standards anyway!). Having said which, we came unstuck when we arrived at Caminha; due to fog the ferry to a Guarda was not running. We had the dilemma of waiting 4hours to see if the fog would lift and the afternoon boat would run, or walking up the Rio Minho to join the Central. We opted for the latter, and were rewarded with the luxury of being the sole inhabitants of the 200 bed Youth hostel in Vila Nova de Cerveira!
We only had one day of utterly dreadful Galician rain, stairods on the route out of Pontevedra, which obliged us to cut short the day and stop in Caldas Das Reis (a very pleasant private hostel, newly opened in what was formerly the maternity hospital - can't remember the name at the moment). On such days I was pleased I had worn my old school leather boots as I had the only dry feet in our small waterlogged group, although my 'waterproof' over trousers were found wanting.....
Whatever you decide, I am sure you will have a wonderful time, Bom Caminho!