ICWAI vs CS

There are a couple of professional institues. I would point three here.
ICAI - Institute of Chartered Accountants of India - Responsible for maintaining accounts and also filing with RCA (Registrar fo Companies)
ICWAI - Institute of Cost & Works Accountants of India - Responsible for cost accountancy - usually manufacturing companies
ICSI - Institute of Company Secretaries of India - Responsible that the company adheres to The Companies Act, 1956

As a CA maintaines financial accounts of a company, a CS needs to make sure that whatever a company does is in accordance with The Comapnies Act. As a CA audits financial accounts, CS audits companies in accordance with The Comapnies Act.

If you talk about the easy thing, in my opinion, ICWAI is easier than CS or CA, CS being the toughest of all.
You will find 100s of thousands of CAs in India but only a couple CS'.
CS works with the top management of a company and no company dares to keep him unhappy. :-)

ICWAI is easier but if you want to directly land in the cockpit ... head towards ICSI.

IAS or Gazetted officers are class officers of the GOI or maybe State Governments. It is not necessary that a CS or ICWAI or CA will work for them. But if you get a government job after clearing these courses, you may.

PS: You need to forget everything else if you are heading towards ICSI.