I want an operating system that can be used for both gaming and developing. Is Mac OS the right choice?
Most or all of the software that you've mentioned is available for OS X (except LoL, which you can run through Bootcamp under your Win7). OS X is a nice operating system with a lot of very well designed software, but the best way to see how it works is to actually use it for a while. I have used Linux and I believe that OS X is much more polished but some people might not care about this and would love to have the ability to tweak every single aspect of their OSs. 

All Blizzard games run perfectly on a Mac. I do Android (and iOS through Xcode) development using Eclipse and I have no problem using OS X for all my needs.