I would say having a lactation consultant who can help you immediately after child birth is probably more effective. I didn't have any classes cos I was overseas during the prep time but still managed ok. The thing I find that I didn't have was the contact to the lactation consultant, and missing the few days of window to breastfeed properly really screwed things up. Also, have the double electric breast pump ready, noone told me that and I bought a manual single one and got a scolding for buying a 'toy'. Anyway, bottom line, find some way to have a lactation consultant to help you asap after delivery.
Dr wong boh boi! A lot of mummies highly recommend it