Originally Posted by Sleiph
photoshop if you love having a ridiculous amounts of control over things (Which you likely won't use!)
Sai is MUCH more nice on memory, and can do most of art things you'd want to do in photo shop, minus the tons of photo filters (It IS photo shop after all..).
I've used photoshop and sai extensively and I can say that I prefer photoshop much more. It's level of customization is insane. Then to add on top of that you have all of photoshops features that you can use in creative ways.
Also to the OP if you plan on doing these with a mouse Illustrator might be a good option as well. Many digital artist start with a wacom bamboo tablet.Many people have false assumptions that digital art will make their art better. Don't fall under that category.