For building (riveting, drilling, etc) I use a 1/4 line long enough to cover my work area.
For painting (HVLP) I use a 3/8" line.
Maybe it doesn't matter. I've sprayed with the 1/4" with no problems.
My die grinder and my orbital sander run noticeably stronger with the 3/8 line. I use 1/4" line for my 1/4" drill, rivet squeezer, cleco remover, and pull riveter.
Looks like I overbuilt. Story of my life. Put in 3/4" Rapidair line to my basement and garage and have 3/8" hoses. I have added the 1/4" flexible Cleaveland hose for ease of use the last few feet. And when I cook I always have leftovers...
Hoses have differing flexibilities. I prefer the more flexible ones - to me, with my limited hose lengths (typically 25' or 50') that's more important than size. However, I haven't painted with these yet.
Looks like I overbuilt. Story of my life. Put in 3/4" Rapidair line to my basement and garage and have 3/8" hoses. I have added the 1/4" flexible Cleaveland hose for ease of use the last few feet. And when I cook I always have leftovers...