Which one should choose user and kernel thread

Question

For a program, I only worked with user threads or kernel threads. Which one should I choose?

Answer 1

accessing and modifying kernel threads isn't easy and feasible. It may even crash your system.

Answer 2

If you have the choice between "user" and "Kernel" threads you should always pick "kernel."

There are some completely useless books on Operating Systems that claim advantages for "user" threads. That is total BS.