What kind of occasion are you going for? What is your normal style?
For me I think the Trendy CC is very eye-catching and statement, but it can go well with casual outfits but it definitely stands out. Have you seen cocobeautea's instagram (
https://www.instagram.com/cocobeautea/)? She often carries a Trendy CC with very casual/neutral outfits and the bag is definitely the "statement piece" of the outfit and makes it look, for lack of a better word, very "trendy".
As for the Kelly, it really depends what size and if you're planning to get sellier or retourne. If you get sellier, especially in a lighter color, I think its a similar effect to the Trendy CC. The only difference is some people who are not familiar with bags (which I feel like is actually majority of people, depending on your crowd), will have no idea what you're carrying; they'll just think "wow that bag is nice/eye-catching!", whereas if you carry the Trendy CC, it screams "I'm a Chanel!".
If you go for a retourne Kelly then its very casual and will blend in with your outfit (if its casual) for a very soft and relaxed look. However if I was carrying it as a work bag I would want something more structured, like the sellier style.
I'm over bags that have too large logos like the Trendy CC, so I wouldn't pick this one. But that's just me. I still want to buy a Chanel Coco Handle as I think its more low key.
So yeah depends on your style and what you want the bag to do for you and your outfit. Personally for me its the Kelly