How do I decide between 2 column layout and single page layout for script?
If you're writing a feature film, or television show, use single column script format. Why? Because that is the standard. 

If you're writing a video script for a corporate client, you want to use Two-Columns. 

Using two columns, audio for one, picture for the other, allows you to literally pace the video, like tracks. 

It would look something like this, with line breaks between each video section and audio section. Also, it would bold things like titles, names, key elements, etc. 

VIDEO                                  AUDIO
Black Screen...
                                       Music Track "XYZ" begins...

TITLE
"Video Name"                           We hear a helicopter approaching over the title.
fades to... 

EXT. WHITE HOUSE SOUTH LAWN

We see Marine One Helicopter descend   V.O. "A new chapter in our Nation's history is
into the frame...                      begining... 

                                       AUDIO SFX: Camera/Press cameras going off. 

Close up shots of Marine One landing. 

                                       V.O. "... A new president is arriving...

Shots of the press... on-lookers...

The wheels touch down                  V.O. "... A new direction unfolds..."

Shots of American Flag waving in 
wind.


The reason this format works well is it literally reads "as the video will be produced". Secondly, it is easy for the client to understand... because they can put together how sounds will enter before/after picture elements.

The formatting is a bit more complex, you want to box each item (horizontal line), and different writers have different styles for bold/italics etc. But that's the general idea.