Vengenance is mental weakness, it is a desire you succumb to.
Forgiveness is mental power, you must fight through your bitterness to acheive it.

Justice as we know is artificial, we made it up. Everyone has a different concept of justice and we can twist it to our selfish views. Only nature knows true justice. Whether forgiveness is deserved or not is up to us.

I believe revenge is a weakness because it's only show that you can't control or overcome your feelings. Revenge will take away your joy and everything that is good to you even if you will succeed in you vengeance, you will still remain sad and unsatisfied. Not everyone deserve to be forgiven but I believe we need to forgive everyone not for their own sake but for our sake. Forgiveness is the way to freedom. 

Revenge is definitely a sign of weakness. Real power is when you ignore those who caused you trouble.  But sometimes it also depends on the degree of the trouble or harm a person has caused you.  If it is a crime, we tend to get even, and if the law couldn't give us justice, we take revenge.  It's our defense mechanism.  But revenge is still not good, because it can never undone what has happened in the past.  Forgiveness is a gift to yourself, and it sets you free.  Everything in life happens for a certain purpose.  We might not understand the reasons, but in the end we'll be able to realize.  Then we become stronger as we learn from all the lessons of life.  Some people have very strong conscience and it bothers them everytime they do something bad.  Other have no conscience at all.  These behavior were caused by how a person was brought up, and maybe affected with his environment or influenced by the people around him.  God forgives, so everybody deserves forgiveness but trust is another thing. Just ignore your haters even if they defame you, coz ignoring them would just drive them more insane! :) The world is round and what ever we do, it bounces back to us.  So as long as you can, do more good things in life and always be positive. 

Revenge is definitely not a sign of weakness . but look to the opposite side, revenge cannot give you permanent happiness and peace as usual . Chinese old sayings remarked : to be fair and plain to those people who did bad things to you , instead of forgiveness . Most of us are not saint and we cannot tolerate too much unfair and distress .

I cannot agree you more concerning your mention to forgiveness . I think it is hard to forgive a bad wrongdoer without trace regret  .I believe in eye for eye on occasion as some bad guys need to be punished or a lesson . The court trial and judge is the minimal punishment .  As for your question regarding forgiveness or revenge , I think the best policy is to hear the real hail from your heart . If you think revenge can make you better and make sure it is legal  , just do it . Once you find revenge cannot palliate your suffering , transfer of your mind is an feasible alternative .