I think 1:1 is best for close friends who you have a strong connection with, and groups are better for more casual friends. You can have a group hangout with people who in 1:1 format you'd struggle to converse with. Personally I don't have any of those friends anymore so I don't do group hangouts.
I can relate. For a lot of people, "friends" is someone you might find yourself sitting with at the same table at a group dinner or playing the same board game with a bunch of other people. But meet up with them one on one and you will quickly run out of things to talk about.
