I have the feeling that Catherine will become quite an asset to the British Royal Family and to the country as a whole. She is an intelligent young woman that has known for quite a few years what her future role will be. If she felt that she could not handle, she would have backed out long ago.
Diana was not given that opportunity plus she was very immature at the time of her wedding. Royals at that time didn't even help the child with her role as a future monarch's wife! We loved Diana because of who she was and how she made her own spot in life. Catherine will make her own and we will either love her or not.
It is not a contest. We can love [or dislike] them both for different things. Diana is history. Catherine is present. I personally wish Catherine all the luck in the world in her future undertaking. She will someday be the wife of the King of England. A world known figure! Other Royal families are really not so well known. Most people, with the exception of "Royal Watchers" could not tell you who are the royals of Denmark, Holland, Norway, or Spain.
It will be in history books 100 years from now, whether or not Diana was more popular than Catherine-----and that will only be written from the bias view of the writer. Does it really matter? There have been many prior Royals that were extremely popular in their day hundreds of years ago, but today we could care less about them. They are just a page of interest in a history book as the "wife of or husband or". Diana had her day, now we have to let Catherine eventually have her's. It is life.