They have different purposes. DV is designed for taking data from multiple sources and "mashing it up" to produce insights and identify patterns in data etc. It's more of an end-user type tool.
Answers is more for building structured dashboards etc.
You can use both. If you think of an organization, you would generally have your development team produce dashboards using answers that are pushed out to the users, and then you would give your users access to DV to mess around with their spreadsheets (and whatever data sources you give them access to).
Here's how it is playing out for us-
DV/VA is for business users with little technical knowledge and Answers/traditional OBIEE is too steep a learning curve for them. These people will mostly use Excel data and visualize it. It's somewhat a competitor to self-service tools like Tableau or Power BI, although it does not have nearly the same feature set yet, however it has the fact that's simple and geared towards business user, where as Tableau and PowerBI are dabbling in the data scientist space and most of those features are too complex for a typical business user anyway. Learning DV/VA is vastly easier than trying to learn the ins and outs of Tableau or Power BI.
The problem with DVD and DV/VA is Oracle hasn't truly integrated them yet. DVD is just a desktop tool - limited options for sharing (PDF or PPT export), you can't upload your dashboard straight to OBIEE or online sharing. You can use VA in the on-premise version of OBIEE and share on OBIEE dashboards or send the link out, but the on-premise version has limited features (and performance) compared to desktop.
VD :-Easy Installation
VA :-bit complex ( Require Installation and configuration)
Connectivity (Data source)
VD :- Excel , Saas , OBIEE , OBIEE report ( No Subject area )
VA :- No Cloud , only local DB (Cube and Relational DB )
OBIEE Logical layer :
VD :- Logical query using Datamodel(Pre built analyse only ).
VA :- Utilizes OBIEE logical layer (Using Data Models).
VD :- Through OBIEE connectivity
VA : - YEs
Vd : - 22 visual elements , Analytics(Clusters, Outliers and Forecast)
VA :- 17 visual elements