I know a bit of both engines but I'm wandering which of the two is the better? I want my game to be easily accessible with no need to download a .exe file. It's a small 2D shooter game with only one map so it should fit in really well as a browser game. 

1. Which one is the easiest to implement into a browser?

2. Which one is the better for browsers?

Thanks a bunch

i apologize this doesn't quite answer your question but i would personally use construct 2 or 3. there are a few limitations but i'd say it's an easier engine to pick up even with no experience and it exports mainly to html5.

I don't have any GameMaker experience, but I have made a few small web browser games in Unity. Once your game is finished, adapting it into a web browser game is pretty much as simple as selecting WebGL as build platform, zipping up the resulting folder, and uploading it here on itch.io. To my understanding it uses Mozilla's technology to build for WebGL, so it works perfectly in Firefox. It can be kinda buggy in Chrome, and doesn't work at all in Internet Explorer. I'm not sure if GameMaker works well in those browsers or not.

I hope this helped some. Good luck in your game jam!