Now that we have LINQ, you can create an array with your two values (DateTimes, TimeSpans, whatever) and then use the .Max() extension method.
var values = new[] { Date1, Date2 };
var max = values.Max();
It reads nice, it's as efficient as Max can be, and it's reusable for more than 2 values of comparison.
The whole problem below worrying about .Kind is a big deal... but I avoid that by never working in local times, ever. If I have something important regarding times, I always work in UTC, even if it means more work to get there.