For thargoid hunting, the gauss rifles are peerless.
For regular use, the plasma charger in particular I feel is well worth it over regular plasmas...
-The 'bolt' is faster, which makes it easier to hit targets.
-The regular plasma gives no indication when it is ready to fire again, which results (at least for me) in many 'darn thing won't fire' missed shots. Whereas the charger is very clear - it fires when you let go of the fire button, and gives you a clear charge bar to indicate your charge level, much better feedback.
-It often isn't clear with plasmas if you hit the target or not, the 'burst' is very small. Whereas a plasma charger will create a blue cloud of gas on impact, making it very clear that you actually hit something. (at least at full charge).
Because of these 'better feedback' and 'easier to hit' advantages, me and a few other folks find it a much more fun weapon to use than regular plasma accelerators, thus I highly recommend these things.