I) The BI sector is changing quickly. So a limited product today might be great tomorrow. But I think the cloud future could be fought out between Power BI (Microsoft), QuickSight (Amazon) and QlikSense (Qlik) if and only if Qlik get their act together. Their marketing will have to improve.
II) These are my views after spending only a limited time evaluating these products (a few days for Tableau although a lot more on Power BI). More time is needed if a detailed comparison is done. This is a guide only and some of these comments / ratings may not be correct.    
III) This evaluation was done mainly for a single user with a small degree of complexity. I have installed and used Qlik View (not Sense) in a server multi user environment but excluded this from any comparison. I have set up and tested the free cloud version of Qlik Sense and Power BI. Both were very impressive in this respect but once again was not included when comparing to other BI solutions. My evaluation was based mainly on a small demo of around 400,000 rows and a small number of linked or appended tables. I did not evaluate the pros and cons of a larger multi user environment. Or look in depth at the cloud offerings.    

Update 20 Nov 2016

I have just had a quick look at QuickSight. It has only just been released but after a year waiting it’s a disappointment. It’s closest to Tableau in its approach & construction. But it includes all the weakness of Tableau but even more so. The joining of data is limited. I couldn’t even join tables from the same excel spreadsheet. The expressions are limited. And the sheets are uninspiring and limited. It’s a basic product with nothing at all standing out. Maybe if Amazon massively improve almost everything it might compete with Tableau. For a much lower cost.
Here’s another viewpoint
http://searchaws.techtarget.com/news/450403234/QuickSight-BI-capabilities-limited-but-big-potential-exists
Spice might be an option though. Where cloud based BI tools use data tables uploaded to (or loaded into) Spice to load into their BI solution. For example Qlik Sense could (maybe) load directly from Spice rather than using QVD files (I assume). Or Tableau likewise (as long as Tableau could join these Spice tables). But otherwise I think it’s too little too late. The gap between Sense and Power BI is just too great. Surely no one who compares Power BI or Sense would buy QuickSight?