you also need 50 krogmo coins unless you buy the sword off the AH.

As for which is the best, my preference is Combuster, Voltedge, Glacious, in that order (Acheron is shadow so it isn't really comparable).

To be perfectly honest I prefer Glacius.

For PvE OR PvP.

In PvE; the freeze is incredibly useful. A wave of puppies spawns? Release a charge and try to get as many as possible in the line of explosions = they all get frozen and don't shoot you unless you go in front of them. I routinely use Electron Vortex so freezing the enemies in front of me gives me enough time to safely charge up the Vortex and drop it. Also most things die within one to two charge attacks anyway so the damage status' wouldn't have much time to do much anyway. It's just an amazing tool to keep everything controlled in just the way you want.

In PvP; the freeze allows for execution kills. This is pretty much the only argument for Glacius > Voltedge in PvP though. The best argument 'for' Voltedge is that when they get shocked they lose the second or so of invincibility frames in between getting hit. This allows you to release the charge then immediately attack into them and probably kill them. With Glacius, however, you can spam off charge attacks and if you catch someone in the freeze, then approach them from behind with a charge attack and 'execute' them. Some players will survive, depending on whether they have Hp trinkets or their class, but they will be severely damaged. The only problem to this strategy is that players on your team may, and often will, break the ice with weak attacks. Which sadfaces me.

Shockburst all the way. It can damage everything around the affected monster and often spasms monsters at just the right time to let you get off a few extra hits.