Both products have an active ingredient that is classified as a synthetic pyrethroid, so they really are very similar in the way that they work.
Suspend SC contains the active ingredient deltamethrin and is a bit more versatile when it comes to some pest treatments.
Demand CS contains the active ingredient lambda-cyhalothrin, and it is micro encapsulated which will make it last a little bit longer in outdoor applications so would be the better product for you in your situation.