Working with a Realtor that knows and understands you and your families needs is incredibly important. What is important to you? Quality schools? Distance to your future place of work? Work and school travel times, keeping in mind that driving times in mid-day traffic may not be indicative of your travel times? Crime rates in the area? Area amenities, restaurants, shopping, grocery stores, fast food, etc.? Area demographics - age, income level, etc.?
The housing price per square foot in McKinney is far less then that in certain parts of Plano or Richardson. In addition, there are far more new homes available, but the commute time to your place of business or employment may be extended as well. Having a Realtor that knows the area and can educate you on the difference in commute times to help weigh those factors into your decision is important. For many the drive time will be well worth it for the larger, newer and nicer home, for others the cost of, fuel, and additional mileage on the vehicles will be overwhelming or perhaps the additional commute time will be the deciding factor.
There are so many things that impact the quality of life that your home and it's location have the ability to impact. For most people, buying a home is the biggest and most important purchase decision they make. It is important to work with someone you trust, who takes a true interest and care in your happiness when it is over, and not just in making the sale.