For program play back, which is usually based on your sound card, use the highest your sound card will allow (better sound quality). Now, for transfering sounds or samples to and from one program to the next, it's depends on what that "program" will allow.
For example: I have a digi001 sound card. I can only handle 48khz playback at 32 bit pcm or IEEE stereo float.
I sample with acid pro 6 and the "program" can render at 96khz IEEE stereo float. I usually inport my samples from acid to recycle. If I redener at 96khz IEEE stereo float recycle won't be able to read the file, but if I render at 48khz IEEE stereo float it will.
Now if you plan on burning a disc to listen to on any device outside of your pc you better do it at 44.1khz 16 bit. Most playback sources, outside of your computer, will not read the disc if you do. 44.1khz 16 bit is CD quality industry standard!
Just depends on what you're doing at the time. Experiement to see what your programs can and can not read.
