I use both Tableau and QlikView. Although very different, I really like both solutions. They belong to the new BI generation known as Interactive Visual Analytics.
In my opinion, QlikView has a more intuitive interface for regular users or executives that are not technical experts but the development side is a little more complex. Up to version 12 QlikView did not provide drag & drop features.
If a user wanted to see something not included in the application the new object had to be created by a power user or developer because Qlikview's scripting has somewhat of a learning curve.
On the positive side, QlikView's scripting is a great asset as it functions as an ETL allowing the integration of hundreds of different data sources into the same visual app.
Tableau on the other hand is a lot easier to use for developers, analysts or power users who need to connect, manipulate and visualize data rather quickly. While this makes Tableau a better fit for the more analytical crowd, it may not be as appealing or intuitive to the regular or casual business users as QlikView is.
Tableau has full pivot, drag & drop and drill down capabilities that are great for developers or power users. They can rotate measures and dimensions and graph them instantly using visualization best practices as suggested by the "show-me" feature.
Tableau’s new versions after 8.1 provide a forecasting function and the capability to connect with the open source statistical program R to include predictive modeling.
Tableau versions 9.3 and higher include a Data Interpreter that makes data cleansing, column splitting and crosstab pivoting very intuitive.
Both solutions continue to be excellent. They are positioned at the top of the leader's quadrant in Gartner's 2015 Magic Quadrant report for BI and Analytics platforms. https://www.gartner.com/doc/reprints?id=1-2XXET8P&ct=160204
In my experience the choice depends on the fit with the company culture and the users' profile.
On July 2014, Qlik introduced a completely new platform called “Qlik Sense” that includes intuitive drag & drop functionality. At this point Qlik Sense Desktop is free for personal and business users that need to easily develop analytic applications on their own - with virtually no IT intervention.
It certainly seems like Qlik Sense is an attempt to regain some of the impressive growth Tableau has enjoyed during the last few years playing in the truly self-service visual BI segment.