I like tools that let me drag and drop a bunch of images into my browser, and generate CSS & a single image for me to integrate into my project.
Stitches is my goto tool for generating spritesheets, and I’ll keep using it for complicated sheets made of many small images.
Today, I found SpritePad which lets me manually place the sprites within the spritesheet. Sometimes I think I can do a better job at making a compact spritesheet than Stitches does, so that’s a useful feature for me. If there are enough images in the spritesheet that manually placing them is too much work, than I can go back to Stitches.