What's the best 2D framework/engine moving forward for use in 2019 and beyond? I want to target both android and iOS platforms. I've been using Adobe/AS3/Air/Captive Runtime for mobile development where I have a custom logic framework and just use a low level sprite blit from a texture atlas for all sprites, tiles, fonts, backgrounds, etc, etc where I render every frame back to front, etc. Of Course there are features like alpha, rotation, scaling, batching, etc, but I'm assuming that would be standard in today's solutions. Thank you for any suggestions.

libGDX would be perfect for this.  https://libgdx.badlogicgames.com/

there is also unity  https://docs.unity3d.com/Manual/android-GettingStarted.html

and unreal engine https://docs.unrealengine.com/en-US/Platforms/iOS/QuickStart

and jmonkey engine http://jmonkeyengine.org/

for but for low level sprite with texture atlas  and where you are doing the rendering I would say  that LibGDX is the best

For more traditional 2D, I would recommend Tilengine. This is a fairly capable scan-line renderer coded using C and linked to SDL 2. It performs very well, and can be embedded into other systems. It does not currently have mobile distributions, but it is open source and can be compiled for any platform that supports SDL 2. I've been playing around with it a little in my free time, and managed to embed it into a Unity project.

Because it utilizes a scan-line rendering system, instead of a modern 3D pipeline, it operates almost exactly like legacy video game systems from the 8-bit and 16-bit generations did. This enforces certain restrictions and limitations, but it also provides some impressive 2D performance. For sprite fanatics and retro-enthusiasts, Tilengine is worth a look.

Esenthel Engine - http://esenthel.com/ I just made it free