Mobile gaming is the quickest and easiest way to make money with games - you just need the right idea to go viral or get featured on the App store and you could be making 50k a day (flappy bird). Also the development time is much much much shorter (flappy bird, again, only took 3 days to make) because of the limitations of mobile hardware and the want to keep your filesize to a minimum, there is much less actual game content and longevity in gameplay is acheived by clever use of mechanics, such as endless runners re-using the same scenery assets.
This is of course providing you monetise right, whether you're hoping to make money through ad revenue or selling in-app purchases using a 'freemium' or 'free-to-play' financial model. There is still money to be made through the one-off purchases, but with the abundance of free apps on the App stores you're unlikely to get noticed unless your app is particularly impressive or you have put a lot of effort and/or money into marketing, again driving up development costs.
As for PC and Console, the next generation of consoles are said to be making it easier for independant game studios to release titles on them, although as they are in their infancy this statement remains to be seen, but there is still a lot of money to be had here, although I would tend to go for digital distribution only. It all depends on how much time effort and money you're willing to put into the deveopment process and how much belief you have in your idea. PC gaming is making a resurgance mainly thanks to the mad deals you can get these days due to Steam sales and Humble Bundles (which is also a great way to get your game noticed whilst making a bit of money at the same time!). But the growth pales in comparison to that of the mobile gaming industry. Take a look at this infographic which depicts the current state of the games industry in the UK;
In summary, if you're thinking of getting into the industry and looking to make money, go mobile.