There are a couple of things you have to keep in mind depending on your requirements…
- Unity supports more platforms. Windows Phone, Blackberry, Tizen for example.
- Unity’s store has plugins for more platforms. UE4 can export to Android, sure. But what if you wanted to take advantage of Amazon’s store with IAPs and GameCircle for achievements / leaderboards? You will have to implement those yourself.
- Unity supports more Android devices. I don’t know about CPU / GPU support, but at the very least it doesn’t require as powerful hardware to run. So you can more easily target older devices while still getting good performance. For UE4 to target a ~4 year old device (which is really quite ancient) you need to pretty much be completely unlit or performance is terrible. But let me put it this way: A $200 phone I bought this year can do pretty much anything in small amounts.
- C# vs. C++. Personally, I find there are next to zero tutorials on C++ with Unreal Engine. It’s an absolute pain in the you-know to decipher how things work. Aside from that, it’s just that C++ is a little more typing-intensive.
- C# vs. Blueprints. There’s a neat thing called Blueprints that lets you code visually without knowing how to program “proper”. You can do the same thing in Unity, if you buy a store plugin.
- Writing shaders vs. UE4’s material editor. Again, if you want to visually edit shaders in Unity you gotta buy something to do it.
- I wouldn’t worry too much about APK size unless you are targeting so-called “developing countries” where limited, expensive data is a concern. The Play store now supports OTA downloads (without an obb file) of 100mb as well. This said, last I checked UE4 spit out larger binaries. Unity released an update today which officially supports compiling to C++, so with this new version I’m curious to look at the difference in file sizes now. But UE4 was about 15-20mb more than Unity last I checked.
There are other things to keep in mind like royalties vs. licenses, splash screens, but those aren’t directly related I guess.
