The beauty of a compare/contrast essay or any essay for that matter is that you can be creative. There is not one set point of view that you must adopt. In light of this, there is no preferred point of view. To take one more step, I would say that it all depends on what your compare/contrast essay is on.
For example, if you are comparing two historical movements, and you are writing an academic paper, then you would want to use a scholarly point of view that knows the scholarship and the time periods well--this is third person. If you were writing for a creative writing course, then your point of view can be two people within those time periods and then your essay can be based on their perspectives--this may be first or third person. As you can tell, there is great flexibility.
In light of these points, consider the context, topic and audience. Based on these, you will need to make a decision.