The whale season in Penisula Valdes is sooooo long. It begins in mid-April and ends in late December. The fauna is free to do what it wants, but it is incredible how its behavior obeys natural forces that tell it when to arrive and when to leave. It is possible that at the beginning of April, specimens will be seen and also that at the beginning of December, whales will not be seen by Peninsula Valdes.
Therefore, to answer which is the best time to see whales it is definitely September October, until mid-November. The whale sightings embarked begin in mid-June, but the weather conditions of cold and high wind, take away some points and do not quote when saying “is the best time of the year to see whales”. Between October and November, being high season in Peninsula Valdes prices are more expensive. That is why, if it is about sighting whales, the last fortnight of September is a great time to visit Puerto Piramides or Puerto Madryn, without spending as much as you would spend from the first October.