It's often a good idea to match your soul weapon to your grid. Sometimes you might even need to use the soul weapon to complete the grid. This may involve using souls people don't normally use and aren't familiar with, so I thought a discussion on which soul to use with which grid might be useful. Here's my thoughts, but I'd like to hear what other people think

Lance: Shingen
Bow: Shingen
Axe: Herc
Gun: D'art
Arcane: Morgan (only choice)
Staff: Morgan for bursting, Andro for stability
Hammer: Sigfried (only choice)
Glaive: Sigfried???
Sword: Arther for bursting, Joan for defense.

An issue issue arises when you have a slow team or a glass cannon. Do you want a soul that fits with your team, or do you want to go the other way to balance it out? For example, with fire sword, Joan will slow you down, but with Arthur you may die soon. So I'm not sure which is better there.