Welcome to the forum.
You'd say A lens at this time but you'd probably ended up with a several leica lenses in the coming months, as many of us. I highly recommended you to try 28mm or 35mm first before buy.
Many would probably recommeded you of the Leica Summicron 2/35 or even Summilux 1.4/35.
My first choice with digital M was Elmarit 2.8/28 then 2/35, 1.4/50, 2.5/75, 2/90 then SA 3.4/21. Choice of lenses are vary in style, price and personal taste, so try them before you buy, then you will soon find yourself the perfectly one to fit to your skill and style.