I dearly love my Soundtoys and my UAD stuff - almost all are FX.  They are simple to use and achieve great results!  I love the simplicity of the Arturia plugs too.  
 
I have the eventide anthology package and I rarely reach for it.  I guess the 3000 and the 3000 delays are a bit out there and the original harmonizer - well the world has moved past that technology ages ago.  It is a shame because I love my eventide H9.  And what outboard gear I used to have of theirs was awesome.  Maybe it is learning curve. 
 
Other tough ones - PPG's Wavemapper and Wavegenerator - i have an original Wave (the big one!) and love wavetable synthesis, but the use --- ugh.  Ditto with Iris from Izotope.  I am not afraid of digging into something, but each of these has a counterintuitive UI.  
You?