TIFF files is a very appreciated format since it will save the premium high-quality of your pictures. However, the drawback with TIFF files is that Transparency may not be saved properly, as opposed to the .psd Photoshop Format that automatically saves transparency.
With TIFF files you have to check Save Transparency in the Save As TIFF Options dialog.
Step by step guide:
1: Save your document as TIFF format
2: In this dialog below click on Save Transparency
3: Press ok and you have a TIFF file with saved transparency