I have a 32" BenQ 1440p monitor for my 2018 Mini and love it. There is no scaling if you run a QHD monitor at native resolution, the size of the screen is irrelevant in that respect. However (obviously) text will be larger on a 32" QHD monitor than a 27" QHD screen.
So it really comes down to personal choice, I used a 23" Apple Cinema display since 2006 and was very happy with the text size on that screen, it was 100 ppi. My 32" screen is 92 ppi, so text is slightly larger and that's fine for me.