Delphi or Visual Stadio for writing applications, MS SQL database ?

Only C#, WPF, EntityFramework!
Take care of it, you see how everything is just made for people. In prehistoric times better than Delphi.

As I understand it you're standing on the crossroads between Delphi and C#... I would advise you to move to the side of the platform .Net and C#, because there is much more opportunity for development and self-realization, a huge Toolbox, a large number of libraries, wonderful documentation on MSDN and a great IDE.
Still You asked about the "friendship VS and MS here, suffice it to say that the products of one manufacturer and therefore their joint use is the most logical and convenient.
About Delphi can be noted that it is very convenient for writing of laboratory work in school and at University, but to develop serious applications it is very inconvenient and a little "crooked". And now a very small part of the IT market is interested in developers for Delphi, because most such specialists are needed to support the already written applications and not for creating new software products.
Thank you for your attention and good luck in development!!!

Business app with tablets? Only)) MVC ASP.NET

When is the question, the application is best done in an IDE, where it is most convenient to the developer (i.e. you) is the application to debug. Do what you feel more comfortable and faster just to understand existing code and production of texts.

In addition I will say that for all the shortcomings of the Delphi debugger it wonderful (...was now already in the new versions I do not know).

Will add to @alexeykiselev.
If WPF seem serious, you can write an application in WinForms. But other technologies remain as is. C#+EF a very powerful thing!