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That depends on what are you willing to be, if you prefer system administration CCNA is enough for you and you can extend your knowledge in microsoft or Linux through other courses (upgrade to MCSE2012, RHCE, Microsoft exchange, ....etc.)
but if you are more interested in network administration then it's prefered to proceed in Cisco courses (CCNP & CCIE) and don't ignore the importance of voice and security :D
If you are really interested then goes for CCNA > CCIE and also go for MTA certification
You must study at least on of the advanced technology like Messaging (Exchange, Lync) or System Management (SCCM, SCOM...)