Poor quality font when connecting MBP 2016 to external 27 inch full HD monitor
The quality of the image is dependent (among other things) on the density of the pixels -- how small they are.
A 27&quot; display of 1920 x 1080 pixels will have a pixel density of around 82 pixels per inch.
To give some perspective, your MacBook Pro's display has a pixel density of 219 pixels per inch. The very first iPhone had a density twice that of your screen.
When buying a monitor, it's not just how big it is, but how many pixels it has. The Apple Thunderbolt Display, for example, is 27&quot; but with 2560 x 1440 pixels, so 109dpi. There are plenty of  27&quot; displays with 3840 x 2160 pixels (&quot;4K&quot;), so c. 164 ppi.
The higher the pixel density, the sharper the image and text. You can't really expect great quality from a 1080p 27&quot; display.
Note that some manufacturers specify 'pixel pitch' rather than PPI. Pitch is the size of one pixel, so 109ppi is 0.233mm pitch; 219ppi is 0.116mm.