Not sure which one fits your needs best. If you want to make some pixel art you can use Photoshop but for anything with complicated shapes its better to use Illustrator, it has so many options to create shapes. Photoshop then again, does have a lot of filters you can apply to your images or heck, even create patterns and effects with a few simple actions.
For me, Photoshop was easier to master, I never really mastered Illustrator fully, so I personally stick to Photoshop for the time being. So Photoshop for effects and pixels, and your needed cropping, downsizing, Illustrator for shapes like characters, vehicles and whatnot. I'm sure someone has more to say about this, but it's best to judge for yourself what the programs can do (search Photoshop/Illustrator tutorials) and see if their capabilities fit your needs.