>>The answer may depend partly on the type of app you want to develop. Although a browser based app is never going to look quite as 'slick' as a device specific one it's possible (with for e.g. bootstrap/angular) to do a reasonable job - and cover a wider variety of client devices. You'll need javascript - but, if you use node.js for the backend, then that's all you'll need.
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>I know what you say. I can feel some banking applications and some games are actually browser applications.
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>>Xamarin is a bit pricy - currently $83 per month per platform.
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>I was a seminar at Microsoft Turkey last month, they said that "Xamarin will be free for Visual Studio 2015".

I saw that. Xamarin offer a Free 'Starter' Edition anyway. Unless the VS version includes more functionality I doubt its enough for serious development work....
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>>C# syntax is not as hard as you may think (esp. compared to C++ :-}). On a side note the < T > usage is merely a convention - you can use anything you like (and guidelines suggest using a more descriptive name). IAC, most developers probably never write custom generic classes.....
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>That's just a sample. C# prefers symbols instead of words. I'm an old developer. You know we came from Cobol ages, remember there is even an optional "is" word in Cobol. :)
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>Update: What's your opinion, you didn't give a choice like others. C# + Xamarin or JS + Cordova?

Not qualified to comment - I've never written a native app for tablet devices......

>If I'm not wrong:
>JS eaiser but more slick feel with C#?

Don't think that's true for native apps - whichever you choose then end product would be the same.
For regular browser apps then, in general, the more logic that's handled on the client with js the better....