To be honest, Pixi.js is just my area of specialty. I've been using it for the past 3 years (with about a 1 year gap, so I'm still catching up on their updates) so it's just what I know. Theoretically, it should be easily adaptable to Phaser also; I know there's a lot of similarities.

I've been in contact with one of the Pixi.js developers over the years and he's a genius of a programmer (he has set up a lot of cool 2.5d/3d stuff with Pixi.js) and helped me personally with projects so that adds to my preference too.

Let me know if you get a chance to play around with a2p or have any suggestions :) If you'd be interested in adding Phaser support the contributions would be greatly appreciated as I know 0 about Phaser haha