If no special characters are present, the first method will scan the whole string four times, while the second will only scan it once. Performance-wise, that's the only difference worth noticing, so you might as well go with the second method. But you're probably wasting your effort. Remember the three rules of optimization:
1. Don't do it. 2. Don't do it. 3. Before you do it, complete the app and profile it; the bottlenecks probably aren't where you expect them to be.