Java with spring or c# with asp??

Depends on the purpose, but generally I'd go for the latter of these two.

Both are good, depends on what you are trying to achieve, and what is your budget, C# if not DotNet Core then hosting will be more expensive. But for me I found C# WebAPI + ReactJS to be much faster than Asp.Net Core

.NET generally has better documentation than Java, and packages are better written. Java has a greater number of packages, but they can often require other bits and pieces without documenting as such. I've also found that setting up a preliminary environment is more straightforward in .NET, but that's because I'm lazy and I just use the pre-existing templates.

Just choose the one you feel more comfortable with. If none, choose the IDE you like most. C# if Visual Studio, Java if IntelliJ IDEA.
If still none, use java as it works on any OS unlike C#

In case I want to create a web app that will be scalable through docker what do you suggest?

@Jop- it's far from 100% compatibility. Otherwise, run visual studio on linux ;-)

@littledev @littledev out of those two - java. Docker has longer history with java (or rather: unix) than dot net (or rather: windows)

I have a server running docker for both MySQL and DotNet Core on an Ubuntu 16.10
Also tired SQL Servere.
With docker you have no constraints UNLESS you are using a technology that requires pure windows and your hosting is Linux

@littledev Dunno anything about Docker to be honest :)

It depends on your use case, in general I would go with .Net as I'm more of a "C# guy", but it's really up to you and what you are trying to do!

Java imo but both are nice

I like java but can be a pain in the ass, I'd go with Asp.net Core Web API with angular and async all the things

@mt3o For c# I prefer Rider above all things, maybe except vim

@Jop- Nah, dotnet core is also cross compilant and the cli tools are way easier than java's

Python with django