Always use an industry standard format like tif[f] if you want to be able to open them a few years down the line; use jp[e]g only if you don't intend to edit them.

Even .tif (.tiff) is not a completely safe archive format.

The TIFF standard defines, if I recall correctly, seven separate kinds of .tif files in reasonably common use, along with several others that are almost never seen. Many programs that can open two or three of these formats may not be able to open the others. In addition, the TIFF standard specifically allows "additional parameters" that a program can define for its own use, which may make "legal .tif" files unopenable in anything other than the program that created them.

Adobe Illustrator, for example, in the last version I used, often produced .tif files that cannot be opened in my Adobe Photoshop Elements. I've encountered a couple of other programs that produced "apparently legal" .tif files, but with "proprietary features" that made them unopenable except in the program that made them.

The .jpg format is probably the closest to being a "universally openable" file for correspondence with those who may not have the same programs you do. The .jpg format is, technically, a .tif file that is compressed, but the compressed format is almost universally readable. Although you can COPY .jpg files without loss, if you open them and re-save them, they're compressed again; and the compression is not perfectly lossless. If you open and save a few times, with even moderate compression, some picture detail is lost.

Better editing programs allow you to choose the amount of compression when saving a .jpg, and if a "high quality" (= very little compression) is consistently used, multiple saves can be made with very little loss, although the files are likely to be about as large as the .bmp file for the same image (and sometimes larger than the .bmp - a .jpg file with NO COMPRESSION is possible, but usually is larger than the .bmp.)

Alternate file formats, such as .png or .gif use a lossless compression, so you can do repeated open/saves without additional loss in picture quality, but the original creation of these file types does discard a little bit of image information, so even these are not "perfect archives." The .gif format, in particular, discards a lot of picture information when first created, if it's made from a "continuous tone" image; and it has the added disadvantage of being a "patented process" that requires payment of a royalty by the creator of the program - hence the absence of legal freeware that can create and save .gif files. The .gif is probably the "most compressed" format available, giving a very small file size; but it is really only suitable for "line drawings" with a few distinct colors and no shading of one color into another.

The "gold standard" for getting all the picture from digital cameras (and some other devices like production scanners) is the RAW form produced natively inside the device. Most cheaper cameras and most scanners don't even allow you to save in this form, and even for the "higher quality" cameras that feature a RAW format output, there is no established standard, so each camera pretty much requires its own proprietary program(s) to download and process the RAW format. This means that the RAW format used by your camera today may become obsolete - and unreadable - as more uniform standards appear. Choose a camera maker with some "staying power" if you choose to use RAW format(s).

Most cameras allow you to save pictures as .jpg, and when you select "how big" to save them what you are actually doing is selecting how much compression is applied in the conversion from the RAW format peculiar to the innards of your camera to .jpg.

For most people with "consumer grade" cameras, a "pretty big .jpg" is the best you'll get out of your camera. Recommended practice is to save the image (.jpg) downloaded from the camera in an "archive folder," and make a copy of it somewhere else before doing any retouching or other editing only on the copy. Some cameras don't even allow this, since they "automatically" do things like red-eye correction and other "modifications" during download (especially if you allow their "free programs" to be installed on your computer).

When working with .jpg (and other formats that may have "lossy" compression) a recommended practice is to NEVER USE SAVE. Always use SAVE AS and add a slightly changed filename for each saved version. This allows you to always be able to start over with the "best version you ever had" (i.e. and new copy of the original saved directly from the camera). When you're done with a multi-step edit (which of course you saved multi-times for recovery purposes while taking the multi-steps, each time with a different name) you can of course delete the intermediate steps, and keep just the finished edit.

Converting a .jpg from your camera to a .tif file will lose some of the image detail contained in the original .jpg. If the .jpg is what comes out of the camera, the original .jpg is what you should save.

Generalizations about what file format is "best" usually overlook the fact that each format was created with specific uses in mind, and each has its own capabilities and limitations. Before you can pick a "best" you MUST KNOW the exact and complete intended use, and the programs/resources the user you're advising has at his/her disposal. (And resources obviously include operator skills.)

John