16 and no esteem

I'm 16 years old, I have a twin that I confide in for most of my problems but this time I feel I need more help... I feel like no matter what I do I can't feel good about myself, even my speaking habits have caused me to stutter some!

I'm not good at arguing, as far as I've known I've never won an argument, it really brings me down. :'( I have a good attitude in front of people, I'm very polite but I know when to joke around too

I'm no leader either, whenever I'm given a choice I try to either stay out of it or try to get a way to have both sides be happy, I wish I could figure it out on my own but I feel like whenever someone tells me "the only person who can solve the problem is you" I don't know how to even solve that problem!

Please help...