Universal is throwing everything but the kitchen sink at Potter 2.0. The main ride will blow away anything Universal or Disney has done stateside in the past 18 years. It's a step above Forbidden Journey and will earn its place among the classic theme park attractions. Carsland looks great and RSR is a wonderful attraction but in terms of the "wow" factor I believe Potter 2.0 will win hands down. There will be some amazing "how did they do that" moments and enough immersive thrills that I just don't think Carsland has.
Some of the interactive technologies Disney is playing with for Avatar look interesting. I'm not involved with Avatar's main ride so I don't know what they have up their sleeve for that one. The bottom line is, so far it looks like Universal is going to win this round in my opinion.