What makes a screenplay "better" is the skill and execution of the writer. What determines how fast a screenplay is completed is how fast the writer is with their skill and execution. Thinking a particular screenplay software helps you write a better screenplay is like thinking a fancy gun helps you shoot on target. You are the writer and you are the creative force behind your idea or concept. Picking the proper tools to help you complete this idea or concept are choices only you can determine based on your particular writing needs.
For me, the program I utilize is Final Draft. Why? For my needs Final Draft acts like a word processing program on steroids. Its userface is similar to Microsoft Word with the only difference being it is specific to industry standard screenplay format. In other words, unlike writing a screenplay in a word processing program like MS Word, Once you put a character's name in the first time you don't have to type it again. What happens is when it gets to the section of the screenplay where you type in the character it will either punch it in for you once you type the first letter or a pop up pull down menu will come up so you can pick from the list of characters you've introduced if two characters have the same first initial!
For sections where you would input setting, action & dialogue the program automatically tabs to the proper position just allowing you to just write your screenplay. This is all I need from screen writing software. I don't utilize all of the tools of Final Draft that exist, but they have some cool ones like the double dialogue feature and the notes feature that act like index cards amongst other things.
Final Draft
Movie Magic Screenwriter
Dramatica Pro 4
Power Structure
Dr. Format Screenwriting Software
Write Brothers StoryView 2.0
The Hollywood Screenplay® Screenwriting Software Suite
Hollywood Screenwriter
Sophocles Screenwriting software
Script Wizard
and
Scriptware
provide something for every writer. Each of these screenplay writing software programs is a powerful, stand-alone tool. It is up to you to decide which is more comfortable for you and which fits your writing needs, but remember...all these programs can be are tools to help you complete your screenplay. They do not create characters or ideas or give logic to your story. Only you, the screenwriter, can do this. So click on the link for each program and read reviews from users who have tried these programs and see which one works best for you.