If you are looking at SIEM, now they normally will integrate with SOAR. (Partnership / acquired by the bigger companies (SIEM))
Like Splunk is working with Phantom
Palo Altos works well with Demisto (Cortex)
Qradar with Resilient.
Though most SOAR would be able to work with most SIEM but somehow they do have a preferred one to a certain extend.
If you could - pick up SOAR piece as well. so that you could be more complete.