A lot of MMOs work well with gamepads, either natively (Final Fantasy XIV: A Realm Reborn and TERA) or through third-party software (World of Warcraft). This is very relevant as PC to TV streaming has gotten better and, in many cases, games like FFXIV just honestly play better on a controller. With this in mind, one of the biggest questions out there is if there is anything better than the Xbox 360 controller (or the Xbox One controller) and honestly, it's going to be a no. 

Realistically, to me, the Xbox controller is your most viable PC controller. It's got all of the buttons, most games that support controller support are literally designed for it and if you use any other controller your buttons are going to be out of place, and it's not comfortable to be in. Unless you absolutely can not stand the Xbox controller, I don't honestly see any purpose in not obtaining one, considering the current price rests around $30 and even less when its on sale. 

Now, there are alternatives. You can use the Playstation 3 controller and I think even the PS4 controller now with some sketchy drivers that may or may not install adware on your PC or require complex series of steps to get working. DS4Windows is the currently favorite, but honestly, it's a hassle - unless you prefer the controller layout. That's fine - if you do, look up DS4Windows and get going with it. I actually use this on my computer, but only because I have spare PS3 controller. 

Other alternatives include the Logitech F710 for a full price modern controller at around $40, for gamers who want an Xbox style controller with a different grip and the F310 around $15 or $20 for a very economical controller that is very similar to the F710 and well the Xbox controller. 

I've done a lot of research on this subject and honestly you're going to find three camps. Dualshock controller users, Xbox controller users, and F710 users. People who praise the Xbox controller do so because it just honestly works right out of the box, you plug it into your PC, and you're good to go. Fans of the Dualshock controllers don't mind the extra steps to get it working or the odd compatibility with games, but prefer the ergonomics of it. Fans of the F710 series love how it's basically a better Xbox controller to them, with a better grip. The F710 works with a lot of programs, wireless out of the box without the need for an separate adapter purchase, and can switch between xbox and xinput/DirectInput modes. 

In all fairness, to just mention some alternatives, there is the SteelSeries Stratus XL which is a very nice controller. I've never personally gotten to use it, but it does have very reasonable reviews. The issue is that it's $65 there abouts and is iOS first, meaning it's mostly for gaming on the iPad and iPhone, however, some enjoy it on PC.  

Finally Zhidong makes a series of controllers that are basically copycats of the Xbox and PS controllers. These have okay reviews and are $20, again, not used one, can't talk about it, but as far as I know it's a viable possibility. 

Yet when bake it all down, your best option at the end of the day is going to just be the wired Xbox 360 controller. That's the best of the best, and there is some wiggle room around very similar alternatives that include grip and price, but that still in 2015 remains the champion.