Everyone has their preferences for different reason. Some prefer snug leather that's tight enough to provide level 2 retention, some prefer a looser leather with a thumbreak. Some prefer a well-fitting kydex holster using friction as retention, and some prefer loosely molded kydex with some sort of button release (like the blackhawk serpa holster)
find out what style appeals to him, either functionally or aesthetically. personally, I LOVE the look of a classic leather holster, but I'm better trained in using a Blackhawk Serpa Holster, and I think a lot of folks here will agree with me when I say that it's a VERY popular and secure OC holster.
just my 2 cents...