I use GameMaker myself, and I have delved into Unity, though I haven't got anything to show for either one of those. I own GameMaker Master Collection, so I am invested in it in a sense.
I love GameMaker honestly. The mobile ports are actually pretty good, and are even better if you get the YYC, which fully compiles to native code, which runs faster than even Unity's .NET(Mono) code. But the "normal" version is actually pretty fast too for most games. I couldn't get your game to work on my Firefox(and I didn't feel like loading IE at the moment), but if it is a TDS like it seems in the description, I'm sure it will run just fine on Mobile even in the normal export from GameMaker.
The main "gotcha" that the YYC(Compiler) gets you is much faster executing code. The actual engine itself gets compiled to native code anyway, but your GML scripts would normally get interpreted. So the one thing you would need to avoid would be massive constantly running scripts. For example, a pathfinding AI would be perfectly fine, but I wouldn't run 3d software vertex skinning doing vertex interpolation via GML scripting code.I've done that, and even on windows it is too slow once you get even a single model with a few thousand vertices to interpolate, much less several characters at once. But with the YYC, that exact same code is fast enough even on mobile.
The other thing is not to have too many objects. For example, if you need a particle system like weapon, use a particle system to draw it, as that is much faster than having hundreds of object instances, and then have a single object with an estimated collision mask for the collision detection of the weapon. This also isn't near the issue it was in the past though, because with GMStudio they updated the runner to be native code, so you can get away with several hundred objects at once most of the time, even on mobile, as long as they are doing simple things, like bounding shapes for collision detection, etc... instead of the pixel by pixel, or using physics.
Last thing about GMStudio, the export it has is also to HTML5, not Flash. Is there a specific reason you want flash. I'm understanding that websites like Kongregate now accept HTML5 games, so that shouldn't be an issue anymore.
About Unity, I've pretty much learned the IDE, and I know how the scripting works. As of version 4.2, we don't get any native 2d tools for Unity, so if you want it, you'll either buy one off the asset store, or create your own. Or for simple games, you could just do 3d game with 2d viewpoint and be fine. But Unity is really made for 3d. In the upcoming version 4.3, there will be some 2d systems in it, but it won't be able to compare with GameMaker on the 2d side unless they do a lot more than they have currently advertised, so if you really want 2d, I'd stick to GameMaker. But, Unity has some advantages for you. For example, if you are interested in 3d, it may be better in the long run for you to learn Unity, as for 3d it is really good. Also, I've never used it, but it has an export to Flash. I don't know how good it is though. In any case, I don't know if you'd want to use it, as 3d assets sometimes can be much larger overall than 2d ones, which affects an online export(Flash/HTML5) as well as any mobile exports, especially Android because of the 50MB google play store size limit. Android itself supports plenty more, but the play store's installers can't be larger than 50MB, which makes 3d severely limiting.
I forgot to mention that for Unity Free, you can now export to Android. I don't think you can export to flash though. I also should mention that Unity exports get get expensive quick, especially if you need to pro versions. Just Android Pro is $1500, but since you have to have the Pro Windows/Mac version, you have to pay $3000 total, and that doesn't include even the Flash export as far as I know. In fact, I was just looking at the website of Unity to confirm, and I can't even see the actual Flash version anymore. It may be that it was a developer preview, I don't know. But I do know that the Unity Web Player export comes with Unity Pro, and I'm not sure if it comes with Unity Free, so Unity is looking to be more expensive in the long run for your basic needs than even the $800 Master Collection of GMStudio. I honestly think that unless you need the 3d features of Unity, GMStudio is going to be much better in the long run, including a win even in the price, since you are interested in multiple platforms. Also, you get with Master Collection the whole group of exports, so if you later want to port to iOS, you can, and Windows Phone, HTML5, Tizen, actually overall more platforms than Unity. I think only Stonetrip's Shiva tool has more exports than GMStudio.
Edited by kburkhart84, 08 October 2013 - 02:37 PM.