Double quotes and single quotes around variables. Which one is faster in SQL query?

I think you are focused on the wrong area for speed optimization... The only thing that will slow you down when trying to decide between single vs double is the fact that you are spending time trying to decide between one or the other... The performance gain or loss is so insignificant it is NOT going effect the end user... I'm sure there will be some nerd that will now come along and say "Not true!! It will be 0.00000001 seconds slower!". Seriously... move on this concern is a waste of time.