The perfect introduction? I don't know that there is such a thing, but there are several ways to begin papers which are effective. All of these include a "hook"--a way to interest your reader and make him/her want to keep reading. You can do this with a quote, an anecdote (short story lead in), statistics, some shocking fact or statement.
The typical formula is to hook the reader, state your purpose for the paper, then spend the next few paragraphs giving reasons for your stance on a subject or factors/steps in your explanation or how-to approach. The conclusion should reiterate without completely restating your main points, since the last few paragraphs are what your reader will most likely remember. Be sure to emphasize the main points in a clever and interesting way.
With comparison and contrast papers, you can organize it one of two ways: first, you could list 3-4 ways the two items resemble and/or differ from each other and then take each of these ways and discuss all the similarities/differences at once before moving on to the next factor, OR you can talk about one of the items and discuss all of the factors you've decided to use and then move to the other subject and do the same thing.Good luck!
I personally have never much cared for 'compare & contrast' papers. My feeling is usually, "so they're the same and they're different. So what?" Nine times out of ten, my feeling is right...
A good introduction for me is a sentence that engages the reader immediately. Often, a quotation from the text works well, or a personal story that can be tied into the text. A sound thesis, one that is engaging and promises to offer a new way to look at something, is crucial. Then the writer (at least young ones) should tell the readers the subjects s/he will be discussing in relation to his thesis for the body of his paper.