My main three were Lightning, Hope, and Fang, so I really only remember what I did with their weapons.

For Lightning, I used the Lionheart, which gave a boost to the Stagger charge. I kinda regretted it after upgrading it a lot, though, and wanted to switch to her speed-boosting weapon (I think the one Karifean was talking about).

For Hope, I don't remember the name of it, but it was whichever one provided the highest magic stat without any penalties. I ignored the ones with abilities and just tried to enhance Hope's already high magic stat.

For Fang, the choice was easy: Taming Pole. Great strength and magic stats, and the only downside was the Stagger Lock, meaning she couldn't cause Stagger (but could still help build the charge). I found that the negative downside of having one person with Stagger Lock was negligible, and was far outweighed by making Fang a more effective Sab and Rav (in addition to the strength boost that could be found in some of her other weapons).