The best way is to build a responsive website. This way you don’t have to maintain seperate versions and sub-domains. A big plus of this technique is that it’s based on media-queries which auto-detects the screensize of the visiting device and shows only the parts suitable for that device. So no need for complicated device scripts.
I build them with Dreamweaver, but there are many responsive templates for WP as well. I know Flytonic has one called the Overlay Theme.
Happy building! 