I know it is a kind of broad question but any answer are appreciated.
C# and Java are easy to move between, although I don't know many people who are experts in both.  C#'s syntax is based off of Java, so they read very, very similarly.  They both run cross-platform; Java on the JVM, C# on .NET or Mono.  They're both OOP, and widely used for web development.  I'd use whichever the team was more familiar with.
Python's off to the side there.  It's also used frequently as a scripting language.  It can use classes and object orientation, but isn't forced to.  It's not as well supported for web work.  I'd use this for a different set of tasks than C#/Java.
How Similar are Java, C#, and Python?