Here  a script you can use to test the 3 methods.

There is a measureable difference between the convert to varchar and the other 2 options.

Only when you increase the number of iterations > 30,000 do you start to see the speed improvement of the last one

(dateadd(datediff)) but as others have said for a small number of conversions any will work - as long as you take into account the locale specific needs for the varchar option.

Kevin

*****************************

declare @loop int, @d datetime

declare @lMax int

set @lMax = 3000

declare @dStart datetime, @dEnd datetime

--various methods to strip off the time portion off a date

set nocount on

set @loop = 1

set @dStart = getdate()

--uses convert

while @loop <@lMax

begin

 set @d= CONVERT(datetime, CONVERT(varchar, getdate(), 101))

 set @loop = @loop + 1

end

select datediff(ms, @dStart,getdate())

set @loop = 1

set @dStart = getdate()

--uses cast

while @loop <@lMax

begin

  set @d = cast(floor(cast(getdate() as float)) as datetime)

 set @loop = @loop + 1

end

select datediff(ms, @dStart,getdate())

set @loop = 1

set @dStart = getdate()

--uses datediff, dateadd

while @loop <@lMax

begin

 set @d= dateadd(d, 0, datediff(d, 0, getdate()))

 set @loop = @loop + 1

end

select datediff(ms, @dStart,getdate())

set nocount off