Does your organization use both Storyline and Captivate? How do you get the most value from each tool?

I agree with everything Lily said but would add: 

Stability of multimedia. Captivate handles media (video/sound) far better (IMO) and it is rock solid in terms of stability.

Fluid Boxes: You can create true Responsive projects, in a single app. unlike StoryLine (They work on any device size)

Extendability, there really isn't anything you can't do if you are willing to bring in some capable Javascript coding talent.  

 I have made the observation in the past that Articulate is like owning an iPhone, while Captivate is like owning an Android phone. If you like the "walled garden" approach of Apple then Storyline may be your thing. If you need more control for customization, stability in both course and LMS integration, and many more technical and creative options then Captivate will work for you.

Cheers,
Steve   

I am not using StoryLine for several reasons, but I know you want an opinion of someone using them both.

Some of my reasons are:

• software simulations are much easier in Captivate
• real responsive projects (not rescalable projects) where the content not only shifts location but can be adapted to different screen sizes
• reusability: I never liked the copy/paste routine, Capitvate has a library, you can use external libraries, where not only assets can be stored but also the shared actions for reusing in other projects. Have a look at: Internal and External Libraries - Captivate blog
• roundtripping with other Adobe applications: Photoshop, Audition, Illustrator, Animate and easy collaboration with Typekit, PhoneGap, Acrobat
• Captivate comes with Video Demo functionality, can be called a small sister of Camtasia, but with fine integration possiblities in a normal Captivate project.
• If you looked at my blog, you would see that I love the advanced and shared actions (point-and-click interface that will be converted to Javascript on runtime); to extend the functionality, using JavaScript- which has become easier since Captivate 8 - has become the way to go.

If you are used to base an eLearning course on Powerpoint, definitely use StoryLine. SL has a great supported community, in Captivate we are still busy building that community. BTW I am just a user...