The short answer is do it right now with whatever tools youve got and learn what you need to learn to get a Rails app up and running.

Your OS doesn't matter so much when you're first starting out. It'll matter later on when you get the hang of some more intermediate to advanced concepts.

My belief (and a question like this will solicit only beliefs from everyone even if presented as facts) is that you probably want a Unix-like OS if you're getting into any web development. The only exception to that rule is if you're going to be primarily using Microsoft technologies like .NET, C#, IIS, or any other number of MS technologies.

I'll give you a rundown of what I've found the best uses for each OS are. This is coming from someone who prefers a Mac (used at home) and uses both Windows and Linux at work. So I've got a lot of experience with all 3 and have used them all for heavy web development projects.

Windows is just fine to start with. You have access to a lot of high level and mainstream tools like code editors and graphics programs. If you're a point-and-click kind of person you'll have no problem. Problems start to arise when you need to set up a local dev environment that would resemble a test or prod environment. You have to jump through hoops and install non-standard programs to get things like Rubygems, and different Ruby versions running locally. It's not difficult per se but you'll find out what I mean when I say its a hassle if you use any other OS. Also, the command line is sorely lacking on Windows and even tools like Cygwin leave something to be desired at times.

Macs are a great alternative to Windows and my
Preferred OS for web development. You get a beautiful interface that's relatively easy to switch over to from Windows. You still get all the power of GUI tools plus the vast majority of Unix-y tools under the hood. It's great for design (you can run Photoshop and other great tools natively) and you get equal or better variety of code editos like Wondows. Where the Mac really shines is once you start playing with the terminal. You've got almost all of the Unix tools you'd have in a prod environment installed by default and you can run things like RVM, Rbenv, and server stacks like AMP (apache, MySQL, PHP) or Nginx instead of Apache and generally just replicate a standard Ruby stack locally through the command line like you would in Linux or with MAMP-style programs. It lacks a decent package manager but tools like Homebrew take care of that for you. Macs, to me, are like Linux distros with top notch desig tools (and minus the freedom but I'm not speaking philosophically here).

Linux distros are very similar to OS X in a lot of ways but have extra Unix tools pre installed that a Mac doesn't have (but can get). They're not always the prettiest and its rare that a designer prefers them (I mention design because for me its a standard part of development) but they're usually the most powerful when it comes to the 3 main OSes out there today. By power I don't mean speed and the ability of the software to take advantage of the hardware. I mean it gives you powerful tools and an unspoken but understood "Unix Way" of doing things. There is a bit of a learning curve however. A local development environment on a Linux machine will most likely best mirror anything you'd publish online.

I went from Windows to Mac to Linux when I was learning web development. Windows let me jump right in with the real simple high level stuff but then gave me trouble when it was time to get more advanced. My Macs let me get all the way to an expert level and never got in my way. I was actually able to learn a lot about how Linux works on a Mac and transfer those skills over so when I got into Linux I was very comfortable. Linux taught me even more valuable skills, many of which I brought back to the Mac.

In the end I chose Mac as my preference because for me its a great middle ground between the absolute raw power of the Unix Way and its great GUI and support for design tools. I could use Linux and Mac with about equal ease and efficiency but Windows still cramps my style to this day no matter how much effort I put into learning its tools or "way" of doing things.

My advice to you is to worry about this decision later. You probably don't have enough experience to know what you're missing and what you'd prefer. And before switching from Windows to anything else just try what's out there. Macs always look great in theory but wonderful as they are they're not always for everyone. (I do have a feeling you will make a switch one day to something other than Windows no matter what - I say this because I've seen it many times and its not common for a web developer to prefer Windows unless, like I mentioned, you're using a primarily MS-based tech stack).

The views expressed herein are my own and not meant to start a religious war over OS choice. To each his own and there aren't any right answers.