Depends on what the gun is for. But I'm a big fan of older guns, trapdoors, Sharps, lever actions, Ruger Vaqueros (I know, modern, but close enough) ...
Basically anything I can load with black powder is fun and good to go.
But, those are competition and fun guns.
For carrying, I go with convenience, thin, light, durable, reliable. I dont care if it is pretty or ugly, the job of a CCW is not to make a fashion statement.
In rifles I prefer wood. But, if it will be a gun used in some sort of competition where it will get wet or covered in mud, I prefer plastic.
Everything has its uses.
For holsters ... Kydex all the way. Unless it's a cowboy style holster, then leather.