I (and a number of other folks) have also run into an enormous memory leak, apparently originating in jpeg-js, when using jimp. On the order of "loading a 3MB file leaks 200MB of memory", which makes it unusable if you're at all RAM-constrained. Shame, because it has a lot of promise otherwise.
Does node-canvas allow you to select high fidelity algorithms over fast algorithms? A while ago, I wrote a crop tool using browser canvas, and found that the results of a scaling operation were unacceptable, due to its fast downsampling algorithm.
The gory details and a few attempts at higher quality scaling algorithm implementations are on SO: http://stackoverflow.com/questions/18922880/html5-canvas-res.... TL;DR: sending the image to the server and having GM scale it is faster and more reliable than your own scaling algorithm in single-threaded browser JS.
