Best Weapons for Specific Roles

Hi. I was wondering if someone could tell me, simply, which Tier 1/Tier 2 weapons are better to upgrade for specific roles for each character, and why. I've found plenty of pages where people sort of discuss what they think is the best weapon for each character, but they rarely say how they're using each character, so it doesn't do me a lot of good.

The way I intend to use each character at the end of the game this time around is:

Fang - Commando
Lightning - Ravager
Sazh - Ravager/Synergist
Vanille - Medic/Saboteur
Hope - Medic/Synergist
Snow - Commando

If someone could break it down for me, I'd greatly appreciate it.

If you're using a character in a single role, you're not playing correctly. I'm sorry to be harsh like that, but it's the truth. The reason all the talk is about "which weapon is best for which character" is because roles are fluid in combat. In most of the difficult fights, especially end-game fights, your characters will not have fixed roles. Each character will have their role shift between two or three roles, on average, in every combat. You need to be able to switch to multiple Sentinels to block heavy attacks, multiple Medics to get back up from heavy attacks, and multiple Soldiers and Ravagers for dealing damage, in addition to having the buff classes. I don't think you can get through the game without ever changing Paradigms and roles mid-combat. It's certainly not the way the game was designed.