it's a very open-ended question... Generally speaking, QlikView is considered the best tool for so called "Guided Analytics", or for high-density dashboards where the presentation should be very particular and where developers have a very high degree of control over the presentation features - Fonts, colors, appearance, show/hide conditions, etc...
Qlik Sense, on the other hand, is better for "self-service" BI, where Users may not care about the particular presentation or having a lot of control, but rather want an easy way of creating their charts with minimum settings.
Between the two extremes, there is a lot of overlap where both tools can be equally good at creating a simple set of visualizations.
Considering that Qlik Sense is a newer tool and is getting most of the development resources going forward, it's safe to say that today most of the newer clients should follow the Qlik Sense path as more future-looking one, unless they have very particular requirements (see the first paragraph) that cannot be satisfied with Sense.
Hope it helps,
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