The reviews I read before I got the game said that, once you'd upgraded your proton blaster completely, it was the best weapon in the game and you wouldn't need any of the other weapons. I'm only half of the way through the game, but I have to say that I'm finding the blue shock wave blaster to be the best weapon so far. The slime shooter is pretty cool, but the stasis stream and the shock wave "shotgun"-type weapon are my favorites.

On professional, it depends on the boss and spirts. The Stasis Stream (blue) is a life saver when trying not to cause too much damage but quickly deal with spirits. All the Ghosts that you can not capture in the trap, I would freeze and blow up. But some of the spirits, like the black slime ones can only be defeated using just the slime blower. The final boss, I felt the Meson Collider (orange) was the best. It was powerful to deplete his energy and spot on accuracy to destroy the energy towers whenever he recharged. All in all, it depends on the situation; all 4 weapons are good at some point.

On casual, yeah the best weapon is the blast stream because ghosts and spirits health is low and they're easier to defeat. Don't really need the other weapons.

for the things that gather enviromental objects together, nothins better than that blue shot gun blast..
and while the upgraded proton beam is a force to be rekoned with, i used to moson collider on the final boss (ALL upgrades purchased by this point) and it seemed to do tons of damage to him, plus i think it was/is his weakness...*scratches head* not sure of the top of my head, only beat it once so far...got other new games distractin me, lol

When he was stationary, I used the Meson Collider on him. However, the proton steam was exceptionally effective because of its accuracy and ability to change direction mid-shot.