It depends on the types of games you are building. Most casual games are pretty much the domain of tablets and smartphones. I’d say that outside of enterprises and content creators, desktops aren’t really in the “in” for majority of the population.
If I had to to pick, I’d go for mobile devices (tablets/smartphones/etc.) when building my games. Or even better, make it browser based…provided it makes sense for the kind of game you are building, of course haha.