Probably neither, at least in my opinion. If you are set on one of those two ways, I would go with the class. But I think the best way would be to make the acquaintance of someone who will sit with you one on one and show you the basics. Then a really good book with lots of diagrams to guide you would be helpful.

I think a class would be lots of fun. And if you know anyone who knits, they could help you if you get stuck. (Or ask here!)

Soon you will be consumed with care of your new baby, and this is a chance to do something for yourself, and it is really fun to learn along with others and laugh with your struggles.