As a person who has taken both courses, I'd take Photoshop over Illustrator. But, I also can't stand to work with that software. Even at work, I'll go out of my way to use either Photoshop or InDesign, even if the original file is in AI.
I use CSP for my comic as well and use Photoshop at home mostly for editing and resizing. However, I used to do my comic on Photoshop for years. I just switched last year. Photoshop has a lot to offer and you can do a lot more than just photo editing. I re-did my entire Animation Demo Reel on Photoshop.I do sometimes still do some paintings/illustrations there too, or I'll flip back and forth between CSP and PS.
Plus, I use it 90% of the time at work. It's the most useful software I know.