What's more exciting? Watching movement in slow motion or fast motion? The answer is, it depends. Depends on the character of the dance. In rumba we're attempting to create contrast between fast and slow. In cha-cha, we're trying to show speed of action. In samba, we do contrast and also fluidity of motion.
Watch the following videos to identify which action is appropriate to which dance:
Samba (also contains routine)
http://www.youtube.com/watch?v=gUSQEVI9hRI
Cha-cha
http://www.youtube.com/watch?v=3iRJtT_ZK2o
All:
http://www.youtube.com/watch?v=kZysO4vDHd8
As contrast, check out a amateur couple
http://www.youtube.com/watch?v=7vjEctvHWgw