Is there any differences between using VB.net or C# in ArcObjects or ArcGIS Server based projects, in functionalities, samples, Q&A community? Is there any comparison which covers these aspects to help choose between them ?
No difference at all. You can start developing with any of those languages that your are more comfortable with. As @Vince has mentioned in the comments, there is one ArcObjects library.
All of the samples are available in both languages. e.g. see here