Well, to deal with any situation.. it's probably recommended that you have weapons of each damage type so you're able to deal critical damage to whatever theme you're going into.

Blazebrand upgrades to the Combuster as its 5*, which is a great Elemental sword.
I don't have any first-hand experience with the Troika lines but from what I learn from other people, it doesn't deal much damage.
Again, I don't have any first-hand experience with the Magnus lines but I hear that the Callahan is good for killing Fiends and such, from a safe distance.

Here's what I suggest (concerning only swords/guns), from my own experience and others:
(these are all the 5* names)

Elemental sword- Divine Avenger or Combuster/Glacius/Voltedge
Elemental gun- Polaris or Magma Driver/Hail Driver/Storm Driver
Piercing sword- Barbarous Thorn Blade or Final Flourish
Piercing gun- Blitz Needle or Callahan
Shadow sword- Acheron or Gran Faust
Shadow gun- Umbra Driver or Biohazard

I mean, that's basically the way I see it.. but honestly, I think it's best if players get equipment that sounds good to them and just experiences the game themselves. More fun that way! :D

Tennis' concise summary tells you everything you want to know. I recommend against Hail Driver. Its shots unfreeze as often as they freeze.

Flameburst's advice is good for swordsmen. BTB is just as good as FF. They differ only in charge attack. I prefer Acheron to Gran Faust, but Gran Faust is also great.

For bombs, consider Shivermist Buster (especially as support for swords), Electron/Graviton Vortex (also as support/party play), Nitronome (for damage), and Dark Briar Barrage (piercing damage). People also like Ash of Agni and Radiant Sun Shards.