Depending on where you are located different certificates may be more important than others.
Because of your first post I assume that you have already at least basic knowledge in security, therefore I won't recommend Security+ by CompTia and similar ones.
Most job offers I saw asked for at least one of the following (in no particular order): OPST, OPSA, CISSP, CEH;
CEH (Certified Ethical Hacker) by EC-Council and CISSP by (ISC)² seems to be the ones one should definetily have on his/ her CV/ resume. But again, if you have only the possibility for one or two certificates, e.g. because of money, it should be considered in which area in security/ pentesting you would like to work. E.g. if you are more interested in malware analysis and research, the GIAC Reverse Engineering Malware (GREM) certificate by SANS may help you more than CISSP.
There are various different areas in penetration testing, so it may help to know in which specifically you are most interested.
In general or if you don't know which area caught your interest most, I would recommend CEH and CISSP.