Unity: A great game maker and one of the most popular ones out there. It has some really good features for stuff like maybe the game Slender for example. The game has really good detail for stuff such as art, pixelation, and a lot of other stuff. But there are some other details that can't be accessed on Unity. Like maybe, taking a background and making it into one of the seeds that can be used for future gamers and, (I don't know much about Unity), sometimes it doesn't give you the option to pick your own unique character. (demo version mostly applies for this)
Alpha: Also a great game maker but not as popular as Unity. It actually can have more downsides plus the same downsides as much as Unity. But Alpha can use less space on your computer. And less space means less viruses! :D But I don't know a lot about Alpha gaming so I might need some help with it. But if you have a slow computer and you're using Unity, the game will lag more than Alpha. Slender is made from Unity. Laggy game for slow computers. Hylophobia is made from Alpha. Almost exactly the same memory usage as Slender but runs a little faster on slow computers. So, which one would you choose?