I have tried both ways (pitching warm and cooling down in the first day or chilling to below fermentation temp and pitching, then allowing to rise to fermentation temperature.) I have had luck with both, as long as the pitch temperature is reasonably close to the fermentation temperature, so there is no shock involved. I prefer to get the wort to fermentation temperature now, but that is partly because I ferment my lagers a tad warmer these days than my old practice (I ferment in the mid 50's for lagers a lot, occasionally cooler). YMMV, so give both a try and see what you prefer.
In my experience, Diacetyl rests are relatively unnecessary when you pitch an adequate amount of healthy, active yeast.