There is no one correct way to do this. That said, if you are willing to use an SPDT switch, a simple RS latch, T flip-flop, and two resistors, you can have a complete solution, including virtually instant, consistently flawless debouncing. You'll be free from all worries of RC delays and inputs that float.

If you want to keep your package count down, the required latch and flip-flop functionality can be obtained from a single dual D flip-flop chip with complementatary outputs and asynchronous preset and clear inputs.

If you want to make sure your "soft power switch" is always off when power is applied, an RC circuit, or even better yet, a microprocessor reset supervisor can accomplish this.

--Sasha Jevtic