Since you've played both, I'm guessing Karin is funner to play than cammy? There was a time where I wanted to main Karin but honestly I don't think I can play a character that doesn't have a fireball. I know in sfv every character has an anti fireball move but I don't know, I want my hadoukens in there lol.
Fun is a relative thing. I 'prefer' Karin because Karin has more shit and that shit covers me being bad sometimes. Like her pinwheel arms (I can't be bothered to learn the real move names, shits complex) as an example. It's an odd move I almost never do, but if I'm struggling to get in or get that last bit of damage, or in a situation where I just feel like it'll surprise the person, I tend to throw it out, and the ability to end it in a throw, OH, or low makes me force a guess when someone is on low health. Stupid, but surprisingly effective even at higher levels of play.
Karin also has her command dashes which cover my inability to walk forward and control space properly. Fuck you, I'll just dash close. Same goes for her excellent regular dashes as well.
I do find her combos the most fun and satisfying of any character in the game. But also among the most difficult as far as just BnBs are concerned. (I said AMONG THE MOST, for anyone getting ready to yell at me about who's harder).
Karin's buttons are great.
Now, the issue here, is I feel like Karin is at her best when played as a whiff punish/footsie monster that transitions into pressure off of that success in neutral. But I don't play her that way. I play her as a hard pressure character that's always going in and trying to stay there, working a tic throw game off my frame advantage (I don't give a fuck what the real definition of a tic throw is or if she does or doesn't have them and something something fuck off.) And trying to crack you open.
....which is essentially Cammy. I like Karin, but if I can transition over to Cammy I feel like i stand to be more successful. Cammy is just MEANT to be played the way I kind of naturally play and she has the buttons to make it happen. I also gain a non-metered AA, more dangerous throw game and since anyone who's played me knows I LOVE me some jumping, a dive kick,, the hooligan flip and soon a super goofy ass air throw.
Cammy also still provides the things I usually gravitate towards in a character, and that's speed and mobility and damage. As much as I like reflector setups and bomb setups and all that, it's just not something I'm very good at.. so I tend to value characters who's strength is straight forward and easy to tap in to. That's not to say Urien's basic combo extension mirrors or ibukis damage bomb combos are hard, but those don't make them DANGEROUS. It's the super long sequences with multiple ambiguous ass guesses that do 75% of a life bar that make those characters truly dangerous, im terrible at remembering that stuff and executing it all when it matters. Characters like Cammy and Karin though, I can just pop vtrigger and make a couple combos hurt more and I'm done.