Which has better background blurriness?APSC 50mm vs M43 75mm

Gerry Siegel wrote:

linux99 wrote:

Fetishising Bokeh is one way to go for taking portraits.

The other is to learn about composition.

+1 for sure. Bokeh is really an obscure or undefined term and when we think we know what it means (creamy bokeh or what have you) as a significant variable, we all have something else in mind depending on our interests or fetishes....Portraits can be headshots or full body shots where subject and surrounds does depend on composition a whole lot... It is true that background appearance (has to be illustrated to define) depends on focal length, size of sensor and f stop.... And more-distances to subject and BG.

That is how I look at the argument of composition control; space background to foreground as a parameter.

We seem to now have a standard in our eye that like other things is a residue of the 35mm film appearance.

Now when I used medium format, the equation changed and ultra fast lenses were not always suitable in portraits. Or affordable....

Lenses now tout circular aperture blades, good for them, and claim to give prettier appearance re circularity of light blobs.
As photographers we are also obliged to take a more sophisticated approach to the subject. But it takes some complexity of mind.

Medium format doesn't actually have ultrafast lenses.  The fastest lenses in DoF terms are all found in 35mm systems (there is nothing as fast as an 85/1.2 or 50/1.2 or 35/1.2 on 645 for example, let alone f/0.95 lenses).

OP isn't clear about whether he means the most blurring or the nicest blurring with bokeh.  They are not the same things.