I've a Mac ( with Windows in BootCamp ). Now I am using Android Studio for Android dev. and XCode for iOS dev. both in OSX. I'd like to get started with Xamarin development. What are the most important differences between Xamarin Studio and Visual Studio? How should I decide which IDE to choose?
I'm not sure if your question isn't out of place on this site. At any rate, Visual Studio and Xamarin Studio can hardly be compared. The former one is a full-fledged, mature juggernaut of an IDE. Unsurprisingly, a bit of a resource hog along with it, still one of the best IDEs in the world.
I used Xamarin Studio on OSX for about a month (just last March). My experience was abysmal. I mean no disrespect for its creators, but I found it:
extremely unstable (crashing a lot),
with lots of irritating visual quirks (eg. the drop-down filenames list for file search popping up beyond the screen edge in full-screen mode, or the text cursor going missing),
user-unfriendly (for instance the ridiculous exception details dialog, in which you need to click your way deep into the inheritance tree only to see the actual exception message)
and far behind Visual Studio in terms of pretty much every functionality I could think of, starting with poor refactoring capabilities.
With latest acquisition, I'd expect things to turn around, but Xamarin Studio isn't there yet. I recommend Visual Studio.