Those of you who answered “Best Wishes,” you’re RIGHT! Always extend your best wishes to a bride, but feel free to say congratulations to the groom.
You may ask why this is...Saying congratulations to the bride implies that she has won something - her groom or that she's no longer being a candidate for spinsterhood. Yet, the groom is to be congratulated for finding his lady, winning her heart and getting her to accept his marriage proposal.
When you wish the best to the bride, you recognize her as the catch, the gem, the object of the groom's affection. Thus, the bride does not need congratulating. Instead, the bride needs a proper send-off for her new life with her husband and your 'Best Wishes'.
To avoid controversy, many people just extend their best wishes to the bride and the groom!