Based only on the information you gave , I think that in general going from a 4 bd, 1bth to a 3bd, 2bth is more desirable to a larger group of buyers and thus more valuable. Obviously, the same motivations that are driving you to consider this change, after living in the home, will be the same for potential buyers. Always keep in mind that the benefits to your family while living there is very important in this decision.... it's not always about the resale value. As stated in previous posts the BEST way to answer this questions is have a competent Real Estate Agent perform a Comparative Market Analysis (CMA), Usually a free service.
I agree more with Becky. There are many factors to take into consideration before making this decision. While a 4BR opens you up to a larger market, most 4BR buyers are going to want two baths. There may be other things you can do with the home to maximize value, and depending on what you owe, what the home could -reasonably bring, when you plan to put it on the market, etc., all of these things need to be adequately investigated. Call me anytime if you need help with real estate related questions: 785-925-3648. You do need a professional to help you with this one!
But you really need to get with an agent specific to your area before you do anything to see where the values are and what is selling.