I've never had them, nor seen them but I never bother looking for them. The daft thing is Jaffa is an orange. So how can you have a pineapple orange? Then again Jaffa is also a brand name so that explains it.
Stick to the Orange ones. Guaranteed to taste great.
My Grandma used to work at McVities, so I shall be the authority. In my time she has bought home, regular Jaffa cakes, Lime Jafa cakes, fully choclate covered Jaffa cakes, choclate cakey bottom bit (instead of the usual white stuff) and indeed, once, pinapple Jaffa cakes.