If I had to choose between spending my time alone or with friends, I would rather be alone. For many reasons for my choice such as relaxing , concentrating and thinking easier (more easily) by myself than with friends. I would like to explain these reasons in the following way.
First of all, the main reason for spending leisure time alone is that I want to be there (in a- I think there need to be a prep here) silent place for relaxing after (a )busy work day. For example, I often read book or listen music for relaxing.. If I spend my time with my friends, we offen talk and my mind is busy at that time so I can not relax completely.
Another important reason for my choice is that when people stay alone, they often concentrate and think (about) their life and future. For example, when I stay alone, I plan my daily works (I think there is no S here) and also what I will do next time. If I spend my leisure time with friend, although I spend good time, I usually need arrange my works and concentate my life. (May be I understand you, but I think your way of express is rather difficult for readers to understand)
From all these reasons above I prefer to be alone because I want to relax, think and arange my works and improve my skills.
I think if you make the conclusion more interesting, your essay will get higher score. Good luck!