You'll find there are lots and lots of factors involved in deciding here.
For example:
Which one are you after: Cloud or On Premises solution
Are you going to index/search only things like app and server logs or also other business information
Do you need user management, access control, etc.
Do you want to manage the underlying infrastructure and ELK on it, or do you want to just call somebody when things break
How much data are you dealing with (think volume discounts)
...
Some options:
Splunk - very powerful, mainly on premises solution, expensive and, if all you want is "supergrep" really too expensive for that use case
DIY ELK - no license fees, but you'll end up spending $ on building various features, either right away if you already know you need N features or incrementally and over time as users start demanding features that ELK doesn't have.
DIY ELK v2 - same as above + consulting/support from Elastic or Sematext to avoid mistakes, help with scaling, provide production support, etc.
Hosted/Cloud ELK (e.g. our Logsene - http://sematext.com/logsene ) - this means you don't need to buy/maintain the hardware or manage Elasticsearch part of ELK.
On Premises ELK (but a version comes with a number of enterprise features, not the bare-bones DIY ELK - see Logsene again)
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