Whatever I like. I might lean towards one brand for revolvers and another for bolt action rifles. These days I would say I support those companies that don't play into the hands of the progressive gun banners.
I have been know to stick with one brand. All have same sight picture, mag release, slide release. It just allows me to keep with doing everything the same each time. Even though I'm shooting a different gun. The one different is my p7 since it is a squeeze cocker but sights are the same, as well as mag release.
IMO there are too many innovative offerings today to remain "loyal" to a single brand. Doing so excludes new designs and technology from your collection.