The first question shouldn't be "which certification should I buy?" It should be "what do I want this certification to help me achieve?" Your answer immediately narrows down the options, whether you want to enter the profession, strengthen your existing expertise, move into customer experience, become a manager, or specialize in contact centre operations or CRM.
A certification appropriate for a frontline professional may be completely unsuitable for an experienced manager. Your destination should influence your certification choice, not the other way around.