I've worked with both systems quite a bit, and really like them both. The licensing obviously makes ELK a no-brainer for my personal use. But, to be fair to Splunk the average required knowledge for their end-user is significantly lower. For the crowd poking around here it seems obvious that ELK is the right choice, but when I am unleashing a team of helpdesk techs on a set of data I would probably have a much more nuanced consideration about the tools.

I'm kind of pointing out the obvious, but it's my two cents for whatever they're worth.