While I can't confirm which is easier, I can say that GameMaker requires a 150$ paid license for web support. However, Unity games in-browser tend to be harder on the player; anyone playing the game needs to install Unity web player, while GameMaker uses HTML5, which most browsers support natively.
Fuuuck $150 for the HTML5 export? I have GameMaker 1.4 Pro but only for Windows and Tizen (For some reason...) export. I originally got it when the base engine was free and pro was half off but now it looks like I made a bad investment.
Well it looks like Unity is my best choice here. Unity web player seems like something most people would download at some point in time. I know I've already got it. Plus it's free to use. Anyway, thanks for the reply!
Unity is using WebGL instead of web player since version 5.3, or earlier. You can play it in most browsers without any plugins.