I was going to say DCA for the exciting rides that appeal to teens until you mentioned that they're used to exciting thrill rides. I'd say you definitely won't have time for both. Therefore, I'd say Disneyland because it has more rides that are uniquely different from other amusement parks. I don't know other amusement parks well, but as far as I know, there's nothing like Indiana Jones, Buzz Lightyear, Haunted Mansion or Space Mountain. Also, even teens can get very excited to walk down Main Street and see the castle for the first time! Disneyland has the true Disney spirit that's not found so much at DCA.
Yikes, it's likely to be very crowded on a Friday afternoon/evening in July. If you can possibly get there any earlier, make it happen! You'll have a great time though--enjoy!