We always liked the futuristic look of the Contemporary tower. After all these years, it is still the only resort where the monorail goes through the lobby. It is too far to walk to/from MK and Poly (at least for us anyway) and I believe due to construction that pathway is currently closed. Walking TO MK from Contemporary is very easy and you have a separate security line that tends to move faster with fewer people compared to the main MK entrance. With small children, we always took the monorail BACK to Contemporary and found being dropped off in the lobby very convenient. Both are great resorts and much of it depends on your budget and personal preference about things like theming.
Depends also on which parks you plan to visit the most. If Epcot/HS are your main interests, I would pick a resort on that side of the property instead.