Preview versions before OS X Lion had more export options than Sierra. By default you can export as JPEG, JPEG-2000, OpenExr, PDF, PNG, and TIFF.

On many occasions I really miss option to export as GIF so after a bit of digging around I came across this little trick; By holding down the Option key while click on Export… it will add GIF, ICNS, KTX, Microsoft BMP, Microsoft Icon, PBM/PGM/PPM, PVRTC, PostScript, PSD, Quick Time Movie, SGI, and TGA as export options. It works on Sierra, and I believe it works on previous versions too.