Unless you are starting your bike under 20 or 15 degrees it doesn't matter. The second number is the grade at operating temps.
When the first number is lower generally it is "better" oil because the add pack to create better flow at very low temps make the oil a little better at start up and "better". I'm not sure this matters either to 99.9% of us who start our bikes at 40 degrees or more.
For those that commute in cold weather, I would go with the best 0w or 5w-40 I could find for the price. Another point in winter its not so important to have the second number be 50 because the outside temp will keep your engine from over heating, the main reason they call for 50 grade. In winter 0w or 5w 40, in summer 15 or 20 w 50.