Best Perks Combos for Each Weapon! Guide and Info.

Basically I want to know which perks are worth keeping and which are not.
As for now I have two epic bigger crit dmg perk, are they worth keeping or should scrap them for gold.
While we are doing this it will be best if everyone get to know important perks for each weapon, so we don't scarp wrong perks.
Let me tell what I know-
1. Sniper- All Crit. Chance perk Sniper Specific one.
Uncommon-2.5%
Rare-5%
Epic-7.5%
With All epic crit chance perks and Talents Max Crit Chance- 45%
2.Grenade- 3 inc. chance for fire and one range perk
Uncommon-6%
Rare-9%
Epic-12%
One Range perk is worth it on Grenade.
Explosive canon-
1. All burn damage perks- if you can set enemy on fire
Epic-12%
2. All damage perks-
Epic-8%
Can anyone tell me perks combo for swift.

 

For explosive cannon it depends on how often you set your foes on fire.
If rarely:

If almost every time