Performance-wise it wouldn't make a difference.

However, to get a TRUE/FALSE result from a where clause like "WHERE var1 = NULL" or a statement like "IF var1 = NULL", you would need to SET ANSI_NULLS OFF.

This is not recommended, since you could end up turning ANSI_NULLS OFF in some situations, and ON in other situations; it will make your queries/applications non-portable; and it can cause you to return unexpected/incorrect results.

I highly recommend leaving SET ANSI_NULLS ON and using ANSI Standard NULLs for these reasons.