I'm a big proponent of grain into water. If you put your water into your MLT first, it gives you the chance to preheat your MLT and gives you the opportunity to make corrections to the temp if you erred - i.e. if the temp is way above your strike, you can either wait or add ice, and if its below, you can remove some of the water and reheat it. I always heat my water to about 3-5df over my strike since that seems to be what my MLT drops the temp immediately.
You can still 'fix' things when the grain is in there, but its messier and now you are running against the clock.