Instructional design

Personal opinion here, but most people that have used both apps would probably say Articulate Storyline felt easier to use.  I feel that the reason for this is the interface is basically a rip-off copying PowerPoint's layout and menus.  People who are very familiar with building presentations in PPT find Storyline quite familiar.

Captivate's interface is really nothing like PPT and therefore requires learning from the ground up.  However, the payoff is that Captivate has deeper functionality in several areas.  I have used both apps many times for client projects, but I always prefer to use Captivate because it doesn't limit me as much in what I can achieve.

Last time I looked, the pricing is roughly similar, with Articulate being the more expensive of the two.  Both are now subscription-based plans.

I suggest you download the trial versions of both apps and see which one you prefer.