All my Websites and WebApps are designed to work beautifully on desktop, laptop, tablet and mobile phones from the outset, so your customers can find you, wherever they are.
This is really important – I’m sure you’ve noticed how much time everyone spends staring at their phones. In fact, Google reckons as many as 50% of web searches – and more than that for local searches – are now done on a mobile device. So you need to be ready for that.
However, “Responsive” is something of a buzzword lately, so should probably be avoided.