Generally, surfing is good in Morocco all year round, apart from April and November due to their rainy weather. The peak surf season lands in December and March when the biggest winter swells hit Morocco from the North Atlantic.
Otherwise for the least stressful rides focus on Taghazout (further north of Agadir) during summer. For more experienced surfers the period from September to March may be the best. Whatever time you choose, you will definitely a lot of fun!