The teacups, without question. I never get to ride them because my girl is terrified of being spun around.
Seriously, I'm not sure anything at DLR would qualify as a thrill ride in the truest sense of the word but that said the above posts are spot on.
DL- Space, Splash, Matterhorn, Thunder Mtn. and Indy
DCA- Grizzly River Run, Maliboomer, Cali Screamin' and Tower of Terror
If you think about it taking an adventurous Canoe Expedition on The Rivers of America could be thrilling for many!