Honesty is my best yet worst quality 
Best because I think honesty requires a lot of courage, worst because sometimes the price I pay are things/people I really care about (people can't handle honesty after all).
What about you guys? 
My best quality would be how extremly good I am at everything.
My Worst quality would be that I'm far too modest.
LOL @irish XD

anyway
I clicked this post thinking I was gonna type mine out, but mine too is honestly. lol
My best quality might be that I'm a loyal friend ^^

My worst quality is having no self-esteem and being too shy xD
Best quality? Hhhmmm. I try my best to look at the brighter side of things. Especially with people, I try not to judge first even when they do something bad.
Worst quality? I think I have a lot lol I can lie really, really well. Plus I'm really cold to other people who don't me. But it's just me being uncomfortable.
Best quality: Value my principles
Worst quality: too anxious/shy sometimes depressed....
Best qualities: I get told that I'm smart...I'm able to solve challenging problems quite well. I'm good at english and mathematics. I can read very fast (e.g. if I have to read a couple of books in a limited amount of time). I can play the piano. I'm not afraid to speak what's on my mind and what I honestly think about and feel for a person (<- this can be considered a good as well as a bad quality)...
Worst qualities: I'm lazy, very introverted. As someone else already said, I can be extremely cold towards people, even those I know well. Usually not intentional .. it's just the way I am, really. Anxiety is a huge problem as well. Wouldn't consider myself shy though..
Best quality: I can keep secrets quite well, i'm quiet most of the time anyway, so that works.
Worst qualities: Low self esteem, tending to overthink everything before taking any actions.. which leads to lack of spontaneity.
I can be impatient. 
Best quality: Perfectionism - I try to make everything the best I can, I put a lot of love and effort in everything I do. If I think I can't make something, I won't do it just so I can say that I did it. 
Worst qualities: Low self esteem. I always tend to think that I am not good enough, and that I should change something when it comes to my personality.
Best qualities: A generally positive attitude and desire to be happy at least a little bit of every day. Also, fierce loyalty and a natural inclination to trust people. Treat me well and don't lie to me, and I'll stand by you for life.

Worst qualities: Self esteem issues here, too. Also, I don't forgive major things easily, or at all. (Little things, absolutely. No sense worrying about those.) Treat me or someone I care about badly, and we're done, particularly if I had a reason to trust you beforehand.
best: trustworthy
worst: impatience and vengeance
Best: Caring nature
Worst:Short temper
Best: Loyalty
Worst: I don't forget and forgive easily
Best: I can easily forgive, I can be easily pleased, very optimistic in life

Worst: my pride like the "you first rule" like if I had a problem/fight with someone they should be the one to approach me first if not your not gonna expect anything from me. Another thing is I easily change my mind