Soft synths can vary a lot regarding sound (...and workflow). Do you favour some combinations which you use a lot in your projects? Seeing youtube videos there seem to be many people having their one workhorse synth they are using almost all the time. Personally I prefer combining different synths in one project, 'cause they can complement each other in their special characteristics.

 

Concept 2 + impOscar + Falcon
...a Combination i like!

 

Something more analog sounding like Diva, with something more digital and clean like Serum is a nice contrast.

I generally like to use more than one Synth in one project, because I think the track sounds more interesting and diverse.

 

I like to use more than one synth plugin for almost the sole reason they are easier to keep track of inside big projects. If you were forming a band, you wouldn't hire 4 guys that all play the same thing, the same way.