A geotechnical engineer can test for expansive clay or other soil problems. With balloon framing the walls are completely different. They traverse continuously all the way from the foundation to the roof - unbroken, nonstop. Each of these framing systems has its own advantages, although today, platform framing is the most commonly used system. Platform framing is easier to construct, less expensive and safer to construct.
Balloon framing provides a better base for stucco and masonry wall coverings.
If you intend to add on and discover that your home is balloon framed, you can still platform-frame the addition. The systems are compatible. Whichever system you choose, be sure to use extra connectors. If the code requires five nails into the end of a header, use six. If it requires three nails in each block, use four.