Hello obx8805dbf, and welcome to cruise-chat;
I don't know if you mean just to Ensenada, or ALL the way down the peninsula, which would mean you are also going to Mazatlan and Puerto Vallarta, which are on the mainland, as well as Cabo San Lucas.
If just to Ensenada, any time of year is fine; it can actually be a little cool from November to March. If you are going all the way down, I would try to avoid Summer and early Fall; it gets really hot and humid, possibility of rain, and an occasional tropical storm or hurricane.
My favorite time for the Mexican Riviera is from February through April. But I also go in October and November. Some people really like the intense heat; and storms are much less frequent or severe than their Caribbean counterparts.
Hope this helps a little.