How to find a good LED screen for your LED displays projects?

You can choose LED Display according to the best view distance (The viewer and LED screen distance):
the viewing distance of a LED display is determined by 2 factors:

1. Pixel Pitch  (Important factor )
2. LED Screen Size

And as for most situation, pixel pitch plays the most important factor for a dedicated LED display. Here's the relationship between the viewing distance and pixel pitch, for your reference:
P2mm LED Display-------------------  Best Viewing Distance 2-24m
P3mm LED Display-------------------  Best Viewing Distance 2.5-25m
P4mm LED Display-------------------  Best Viewing Distance 3-28m

P6mm LED Display-------------------  Best Viewing Distance 3.5-40m
P7.8mm LED Display------------------- Best Viewing Distance 4-42m
P9mm LED Display-------------------   Best Viewing Distance 4.5-50m
P10mm LED Display------------------- Best Viewing Distance 5-55m
P12mm LED Display------------------- Best Viewing Distance 8-66m

P16mm LED Display------------------- Best Viewing Distance 9-75m

P20mm LED Display------------------- Best Viewing Distance 10-80m