I'm not forgetting the Rags but I'm also not going ignore Liverpool, just out of some weird point scoring notion.
Let's get it right too, Liverpool have been at it for more than "just the last two seasons". Anyone saying that, where have you been? Selective memories? They have form for manufacturing rivalries with non local rivals, just by their twatty entitled behaviour, when they happen to be challenging.
They did it with United, they did it with Chelsea(am I missing out Arsenal? I can't seem to remember them challenging at the same time), they started with us soon after our first PL win. It was right about the time when they realised we meant business and the satisfaction of seeing the rags suffer wore off.
As others have said, as a club it's United but you have to blind not to see Liverpool fans are worse, now we've had a taste of it first hand. Our relationship with the Rags is not uncommon as a local rival, given their success we'd have to expect some of the stick they've given(we're not soft, we take it well and give it back). I'd much rather have Spurs or Chelsea challenging with us than Liverpool, Spurs fans can be annoying and way above themselves but Liverpool fans really put them into perspective.