Bladelogic has multi OS support and can manage even the ESX servers along with Templete based provisioning integrating with vCenter (VMWare). Along with this, BladeLogic is based on Push mechanism where the server is active and clients and passive and hence does not use the Memory or CPU until something is deployed.
SCCM on other hand can manage only windows (2007 version) and now with 2012 version, Linux as well. But, that cannot be integrated with VMWare or third party..SCCM client is active and the server is passive..as in, the client keeps on polling the server for any new update if available..(which eats up the menory sometimes)
It would mostly depend on what kind of environment you have..If you have a Multi OS environment and you are only concerned about servers and not the Desktop management via same tool, go for BladeLogic. Also, this can be integrated with most other BMC tools (using Atrium Orchestrator) and third party vendors as well (VMWare, HP, Service now, etc..)
SCCM is also picking up very good in market and is comparitively cheaper.(not sure about the 2012 version)..