Most people I know use gear inches.

It's not that gear inches measure anything particularly useful, but they do give you a nice range with a lot of discrete numbers, which is fairly easy to understand.

My bike's range, in gear inches, is something like 22-100. Dividing my 27 gears among the 78 available inches gives me lots of whole numbers I can use to describe my gears, without requiring the use of decimals.

In gain ratios, my bike's range is 1.7 to 7.5, approximately. I still have the same 27 gears, but now I'm dividing them up among 5.8 spaces (rather than 78). Although my bike travels the same distance in any system, for me it is more intuitive to think of some of my lower gears as being 26, 30, 31, 35, 36, etc. gear inches, as opposed to having gain ratios of 2.0, 2.3, 2.4, 2.7, 2.8.

These numbers are arbitrary, I suppose, and if I grew up using gain ratios, maybe I would prefer it. But most people seem to be used to gear inches...