There is no straight answer for this kind of a question 🙂
WhatsApp Campaigns allows you to send one-to-one messages to your target WhatsApp list.
Group Sender Campaigns allows you to form WhatsApp Groups, Add new members, and then run messaging campaigns in these WhatsApp Groups.
We prefer that when you are running any marketing campaigns, then use WhatsApp Campaigns. And if you are running any campaign that needs more engagement, conversations, and makes the campaign more viral in nature, run Group Sender campaigns due to WhatsApp groups, which is targeted towards forming community and starting conversations around a particular topic.