When comparing Stencyl vs Buildbox, the Slant community recommends Stencyl for most people. In the question“What are the best 2D game engines?” Stencyl is ranked 11th while Buildbox is ranked 50th. The most important reason people chose Stencyl is:
Power users can also write code in Haxe (similar to Actionscript 3) to create their own custom classes and extend the engine.
Specs
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Pros

Pro Haxe scripting available for advanced users
Power users can also write code in Haxe (similar to Actionscript 3) to create their own custom classes and extend the engine.

Pro No coding required, great drag & drop interface
Visual scripting in Stencyl is based on the MIT Scratch project, which was designed to teach programming. Script elements fit together like puzzle pieces, ensuring that data and function types cannot be mismatched.
Pro Cross-Platform
Publish iOS, Android, Flash, Windows and Mac games without code.
Pro It's a NO-CODE Program, you can add logic without code
Pro The original concept for Ghost Song was created using Stencyl
The original concept for Ghost Song was created using Stencyl 3.x
Pro Great performance on every platform
Stencyl exports your games to native code so they have great performance on every platform.

Pro Drag - and - drop editor
Drag - and - drop editor without writing any line of code.
Pro Easy to learn
Buildbox is a drag and drop engine, making it easy for beginners to pick up. There are many tutorials available to help get you started.
Pro Has many game templates
Buildbox has 20+ different game templates including templates for platformers, racing games and Flappy Bird clones.
Pro Built-in support for ads
You can add banner and interstitial ads from multiple ad networks, including AdMob, RevMob, Facebook. They can work with Amazon's, Microsoft's, Google's and Apple's app stores.
Pro Develop once publish everywhere
Exporting iOS/Android/macOS/Windows/Steam/Amazon
Pro Cross-platform
Cons
Con Not a powerful engine
Should be used for basic games only.

Con Only available via subscription
There should be an option to buy it outright, especially considering it is written by a one man team....this is not exactly an Adobe level enterprise with shareholders, so there is no excuse!
Con Slow release cycle
Con Updated
It needs much to improve for mobile games, it was left in the era of Flash games. In Android you can not even put the native keyboard, you can not access things like native camera, GPS or native text input.
Con Tile system is somewhat inflexible
Con Incredibly Expensive
$99/mo for full functionality probably makes this the least accessible piece of game development software in regards to price, all with a very limiting feature set.
Con You are restricted by it's limitations
For example, you can only make certain kind of games.
Con Not very powerful
You will be limited to using templates to build games.
Con Subscription Model
The two more reasonable price points limit the functionality of a software already far less powerful than many more cost effective alternatives.

Con Very expensive
Buildbox has a 15-day trial version, after that a $2675 license to use it must be bought.
Con Stability Issues
The software has stability issues on Windows, with the preview window causing program crashes when simple functionality is added.
