What gets me is the people who automatically say, "Stay away from RT - you won't be happy with it." How do you know? Your needs may be different than the person's who is asking the question. For me, no way - RT won't make me happy. For my wife, an RT tablet is what we're going to get her. It will meet all of her needs. Just because RT doesn't meet your needs doesn't mean it doesn't meet everyone's needs.
As for the OP, there are two questions that you need to answer before making this decision. First is whether RT will meet your needs, or if Windows 8 is what you need. Second is screen size - will the 8" Dell meet your needs, or do you need the larger size of the 2520 (assuming RT is good enough for you)? You can get more granular after that, but IMO those are the first two questions you need to answer before making a decision on a particular tablet. And if RT won't meet your needs, and 8" is too small, then look at other tablets.