I was about to jump on the rumba bandwagon and was deciding which to choose for part two of the question: "Rachel Steven's was good...and Kartem's was okay...and Colin Jackson's was excellent for a bloke...and Cherie Lunghi's was pretty good..." at which point I realised I actually don't mind the rumba.
The cha cha cha, however...it's dull, it's unmemorable, it was a week one standard for a reason, half the time it's indistinguishable from a salsa or samba when done Strictly-style. The only one I can think of that stuck in my mind and that I would watch again was Alesha's, and that is almost entirely because of her channelling Beyoncé in the opening bars where she looks FIERCE *does z-snap*