I need to know?

The "which engine is better" question gets asked here probably once a week. Try looking up some of the old answers for something more in-depth.

I've used unity for years and have become quite annoyed with parts of it, so I've done some moderate research into alternatives. My biggest problem with GameMaker studio is that it uses its own language which is pretty much useless outside of that engine. This alone kills it for me. I've also read that it has alot of its own problems and some pretty severe bugs.

I've used both. I also mention that they just announced the new Gamemaker Studio version 2, which is actually even better in quite many ways than GMS Master Collection, so I wouldn't purchase it at this time, rather wait until Q1 of next year.

As far as the engines themselves...the usual answer is that it depends on what you want, and your budget. Honestly, if you are interested in 3d, now, or in the future, you are probably better off with Unity. GMS has a couple functions for 3d, but it is not really "part of the engine." The room editor is 2d only, there is no native 3d resource systems, and no 3d animations at all. You can code all this, as we can create shaders. In fact, there is currently both a deferred rendering pipeline and nice 3d model skeletal animation being done. But it is something extra, not included in the engine. Unity, as it is primarily meant for 3d will take the cake in that department. It has animation, special effects, the editor, 3d asset usage, basically all you need to work in 3d except the assets, and some really high end stuff. In fact, I would say that unless you are interested in multiple engines(cuz you have time or whatever), you would be better off using Unity even for a 2d game, as to invest your time in the engine that you would likely be using later for 3d.

Now, if you only want 2d, and will never be interested in anything but 2d for the foreseeable future, the GMS will win in pretty much all cases. The GML language that SirWeeble mentions is indeed proprietary, but the truth is that it is a pretty simple language, especially if you have done any programming in any C-Style language. You would spend more time just learning API/functions/IDE than the language itself. Now, if it is the first language you would learn, it will take longer, as you are learning both syntax and general concepts(like do/while, if conditions, variables, etc...). But for me, the fact that the language is only useful in this one place doesn't bother me, as I have no problem learning a language for a certain purpose....my brain has plenty of space.

About the engine/software...it is much better for 2d than Unity is. It is automatically "pixel-perfect" while Unity is not. It comes with some features that Unity also has, like the 2d physics engine, but it goes much farther, having a dedicated tile engine(which is getting revamped and better in GMS2). It has 2d pathfinding functions(and you don't have to worry about which axis you are on like in Unity's internal pathfinding). The engine is "2d optimized" behind the scenes, with things like texture pages, which take all your sprites and put them onto single textures like a texture atlas, allowing the engine to draw things quicker with less texture swaps to video RAM(great for mobile more so than desktop). But on top of these nice features, you have some higher end things as well that aren't in other "2d" systems. You can access much of the rendering pipeline, drawing multiple views/cameras. You can do render textures(drawing to a texture, than using that texture as part of another drawing even on the same frame), though GMS calls them "surfaces." You can use your own shaders for many things, including normal-mapped sprites, lighting engines, or as I mentioned above, 3d stuff). There are also things that Unity has in some form that GMS also has. Unity has the animation system, in which you can call functions at different moments of the animation. GMS has timelines, which do basically the same thing. GMS also has "paths" which you can use as waypoints for objects to travel along, though there are other uses as well, basically anything that needs interpolation between a series of points, say a writhing tentacle or chain...Unity doesn't directly have this, but you can get iTween which has something like it, or many of the asset store things also do it.

Now, I can mention some cons as well. While Unity is excellent for 3d, the 2d side is pretty lacking. There are some other higher-end features that are also lacking(mainly in the rendering department). The average indie developer won't notice this lacking, though a AAA studio very likely would. Many of these shortcomings can be overcome with the asset store. That thing is HUGE.

GMS is also not without flaws. For example, the particle system is pretty lacking. It works pretty well in general, but Unity's is better. Unity has forces, attractors(repellers), and colliders, which GMS's particle system lacks. It can also use full on gradients to describe particle details(like color over lifetime) while GMS can only use 3 points to create the gradient for these things. GMS also has the higher price point if you are interested in mobile development. Unity gives you all of that stuff free in the personal edition, while GMS does not. Also, GML vs Unity's C#...GML is pretty neat, and actually really quick to work with because you don't have a lot of the things that you have in C#. But by the same token, you don't have those things in C# that can be pretty nice, like classes(with methods), different data types, coroutines, and many other things. GML won't get in your way as far as actually coding your gameplay, but it just doesn't have some of those features. Once you figure out how to do the things though, you can still do pretty much everything you want, just you have to do it the "gamemaker" way.

If you want to make something which will look decent on Steam or on Google Play then Unity is the way to go.

I need to know?

They are both systems for making games, but otherwise not really comparable, in particular for an ambiguous qualification such as "better" (my "better" is likely different from your "better", which is again different from "better" of everybody else).

Read about both systems, look at examples or demos (keeping in mind those are likely beyond what you can achieve), and use them for a week to make a simple game or so.

Then you are in a far better position to call something "better" (for your value of better).

Try to read this old threads. http://www.giantbomb.com/forums/general-discussion-30/unity-or-game-maker-studio-1490907/ you can get some alternative from there.