JPEG - Fairly high/decent quality, however it compresses the image size and flattens the image, suitable for saving experiments. 

PHOTOSHOP (PSD) - High quality, large file size, saves and keeps open all layers, this format allows you to keep working on the image. 

TIFF - Very high quality, ideal for saving final/best/important images, won't compress the image at all. 

RAW - Not recommended, high quality, large file size.