So well I have made a fair bit since I last actually considered this so obviously my favourite has changed (what with improvements in general quality, etc.)
So here's my new favourite one so far:
Probably nothing too impressive but I like it and it looks cool so eehhh soddit it works
[color=#30c08f]I take it you're using MS paint and a mouse.
tbh if you're being at least semi-serious about it I'd recommend getting a different free paint program like GIMP or Paint.net. It's no SAI but it does the trick.