Every single vagabond or keen traveller is not going to hesitate at all while answering this question. To travel alone is the best! All of the great travellers I know travel alone and it is not possible to persuade them that it can be really nice to travel with a group. And they are more or less right. The greatest travelling projects I’ve ever seen are always done alone. When you travel alone you have to meet people and to talk to local people. No one can survive without social contacts and communication with other people. So travelling alone is more or less a way to concentrate on the travel itself and on the local people and to make contacts easier. You get no distraction at all. And it is great when you meet on the way another travellers, because you can shortly exchange or travel some days together and then go again your own way. And if you meet them again, than it is almost a miracle and normally a great friendship starts.
When travelling alone, you learn a lot about foreign cultures and landscapes, but you learn mostly about yourself. You experience your limits and have enough time to be with yourself and to start vital changes. This is a great way to improve.
On the other hand, when you travel with a group, you stay more or less inside this group and can’t get the best of your travel. On the other hand you can experience the group dynamic and to understand a lot about the group member. Travelling together is a very good way to make friends forever, but all to discover deep differences you’ve never seen before. If some critical situations happen, then you can learn even more about yourself, the other group members, about the different roles and interaction models. You can learn to help, to consider, to share and to give. And it is of course much more fun to be in a big group.
I personally prefer to travel in a small group, 2 or 3 people. Thus I can experience both the benefits of a group travelling and travelling alone. I like dynamical group member changes as well. Pretty nice way of travelling is to travel for several days with local as well. It’s easy possible with couch surfing and combines its benefits with the benefits of travelling in a small group.