First, GIAC isn't a certification; it's a certification body tied closely to SANS. GIAC produces dozens of different certs, and are generally well-regarded. Second, it depends on what you're looking for. For example, if you're looking for general info, the CISSP is regarded as the standard, though the certification itself doesn't go far to validate actual knowledge or capability--it covers security "a mile wide and an inch deep." But the CISSP does carry a requirement of five years of information security background. I've seen some people with a CISSP that lied, breaching the code of ethics they bind you to. That alone should tell you something about that individual. Another general certification is the GIAC Security Essentials (GSEC).
If you're looking for penetration testing or incident response, the GIAC Certified Incident Handler (GCIH) is a good choice. If you're looking for computer forensics, the GIAC Certified Forensic Analyst (GCFA) is better.
Now, the other "it depends" pertains more to whether you're looking for enrichment and career opportunity for yourself, then having any will help, especially since it allows you to expand your knowledge and experience. The bonus is that it helps show that initiative on your resume. If you're looking for certifications for a new-hire, remember that some of these certifications are trivially easy to get.