The visual editor of playcanva has been one my favorite tools to use with Unity3d so far! It's really easy in creating assets like meshes or UV maps from scratch as well importing them into unity projects (and exporting again).
I have had some problems when trying out new features but it was solved very fast by their support team! If you're looking forward having everything under your control then this tool will be perfect because they offer all kinds of functions which are needed while developing even simple 2ds game prototypes :.