What is the execution plan?
I think both are equal for SQL Server so no matter you will use the execution plan should be the same.
One thing:
If you store time potion in that datetime field and you want date between 01/01/2008 and 01/31/2008 you have to use:
SELECT ...
FROM ...
WHERE DateTimeField >= '20080101' AND
DateTimeField < '20080201'
Just because 01/31/2008 01:03:00.111 is bigger than just 01/31/2008.
Against Stupidity the Gods themselves Contend in Vain - Johann Christoph Friedrich von Schiller
The only thing normal about database guys is their tables.