For anyone without the support of family there is a strong chance that what you leave in your will, will go towards your care in later life (nursing home or carers).
But that apart, I would leave what you have, and no doubt worked hard for, to those that have made you happy in life and are in need of support ie loved ones who have loved you back, people and charities that are close to your heart (eg heart, cancer research, water aid, dogs homes etc, but not to those that spend unwisely, or to people with plenty of money of their own. Include a note that you have chosen not to leave money to anyone who has not been part of your life, including family, in case they contest it,and if you are looking at more than a few thousand (after funeral costs), use a solicitor.