That's a tough question as it really depends on a prospective Buyer's needs. That response is assuming you are looking at two homes that you are equally attracted to and that you are seeking input to help you break the tie in desirability.
My experience is that most Buyers will like having a full bath off the MBR instead of a shared bath between bedrooms. I'd venture to guess that easily 80% of Buyers might agree with me on that. The other thing to consider is room sizes. Often, a 3 bedroom home will have larger bedroom sizes than an equally sized home that has a 4 bedroom configuration.
Hope this helps.
Greg Hanner, Broker, REALTOR, e-PRO