This is a very important decision that needs to be taken by the organization. There are both commercial offerings as well as open source offerings that are available today but the amount of efforts that need to be taken in each of them varies a lot.
I have seen many commercial offerings such as Splunk and ArcSight being used in large enterprises, including national level banks. On the contrary, there are also open source offerings, such as ELK Stack, that are gaining popularity especially after Filebeat got introduced.
At a personal level, I really like Splunk but it gets very expensive when you have a lot of data being generated. This is one of the reasons why many startups or mid-sized organizations use commercial offering along with open source offerings such as ELK Stack.
Having said that, we need to understand that if you decide to go...