I used to have strong preferences in ye olden dayes...didn't like the rumba at all for example...but now it really depends very largely on who's dancing.
I find it depends hugely on the dancers. I was never a fan of the waltz til I saw Hayley Holt do it last series. Similarly I loathed the foxtrot til Jade and Ian's one last week.
As a rule I adore the jive, and find the salsa a bit of a joke.
I'm with alot of the majority in that it does depend on the dancers; my least favourite is usually the Rumba when danced by the contestants as it's often cringeworthy IMO but after seeing Matt&Nicole Cutler dance the Rumba live I love it.
My favourites are the Quickstep and American Smooth, preferably with a classic song to match (Frankie or some such).
Least favourite would be Rumba. A bit dull and not my cup of tea really. Not too keen on Tango either as some of the faces the slebs make are downright bizzare
Faves: Jive, Paso, American Smooth (when they are done well)
Least Fave: used to be Rumba but have grown to like it so is now Samba as it is almost always dreadful! Only Sambas I've ever liked were from Zoe&Ian, Mark&Karen, Jill&Darren, Alesha&Matt and Denise&Ian.