Thunder is def a must and T3 on your bar for when you get thundercloud procs.
Lethargy.. well you have another attack/spell that applies heavy anyhow it is very situational
Aetherial Manipulation is an absolute must and i use a a macro for it.
Freeze i honestly do not find any real use of it, i guess when introduced it had it's use, not as much now
Sleep is PVP only, no real need to use it in low level dungeons, but good to get a laugh a bit i guess?