Hi Vaibhav,

I assume that you mean better cutoff rate rather than better step response.

Your question is unclear. What do you mean by mapping complex poles on the
real frequency axis??

Use of complex poles allows one to achieve sharper cutoff between passband and stopband for a lower order filter, which means fewer components and opamps etc. Thus, there is a direct cost/power advantage. Regardless of that, you will still place the poles well inside the left-half s-plane.

I would suggest that you look up a book on basic filter design. Van Valkenburg's text is one possible reference, but there is no dearth of those. You can even use the filter design utility in MATLAB to create filters of different order and type and look at their pole-zero plots to gain some insight. An even better way to gain insight would be to pick up a DSP text and look through the chapter on FIR filter design.

You can also look at a recently posted topic "Effect of zeros on filters".

Regards
Vivek