i use photoshop most of the time. I draw my first sketch, then base a set of key frame sketches based on it, i then test the timing between each key frame.
Once i think it looks okay I lineart all the key frames
i check again, and if i like how it flows i add the in between frames using the key frames on a low opacity to trace over to get a accurate transition. I then colour all the frames using a similar low opacity method to make sure it’s accurate