This weekend (13 Jan 2013) will feature Man United against Liverpool. Currently Man City is the main rival of Man Utd, but traditionally, Man Utd vs Liverpool has something extra to show.
As for me, I respect Liverpool as a Football Club. I grew in the seventies & eighties, where Liverpool was the supreme team. During my primary school days, I played for a football team that we call ourselves "Looprevil". That is Liverpool spelled backwards. I used to watch Kevin Keegan partnering John Toshak upfront. Liverpool captain at that time was Emilyn Hughes, with a Liverpool hardman "Tommy Smith". They have Steve Heighway on the wings, and a supersub by the name of David Fairclough. They practically win everything from 1975-1977. The keeper was Ray Clemence.
I consider Man Utd vs Arsenal as a more "special" feature simply because of Mr Arsene Wenger. I love to see him lose his temper..
I hope Man Utd win, and Mr Wenger's Arsenal defeat Man City. That will be the perfect combination.