Construct is a very capable 2D engine, you can take a look at this game we recently released, it's 100% made in C3.
I haven't used Unity, but I heard that certain routine operations (like adding new sprites, animations etc.) are much easier and faster to do in C3, than in Unity.
C3 is an almost perfect engine for casual mobile games. Unfortunately, when it comes to monetization (ads, IAPs), its official plugins are barely adequate. You will probably need to purchase 3rd party addons, for example this collection.