Tascam 701-D Sample Setting KHz

Depends on what you are recording sound for. It's normal to record video sound at 48k, but if you are burning stuff onto a CD then they only run at 44.1k. Since a sample rate of 44.1k gives you an available frequency response up to 22.05kHz, and only bats and a few other animals (not humans) can hear frequencies that high, there's no point with modern equipment in using 96k or 192k, because all you will be doing is storing a lot of noise. And also, this will make your files 2-4x larger than they need to be! Microphones that can record frequencies significantly above 20kHz are also pretty damned expensive, and very little in the natural world produces any meaningful output at those frequencies - except bats. And if you want to record bats, you need some specialised kit to do it with anyway...

So the answer is, as I mentioned - it depends.

Also, strictly speaking these numbers aren't kHz either - they're k(ilo)samples/sec.