Ahahah yes @christined is spot on, I love the 12% for being more lightweight, yet still very effective.
I prefer to recommend Vitamin C for its antioxidant effects rather than its cell renewal properties - the stronger the Vitamin C the more exfoliation you’ll likely get, which can be extremely effective for some people… however if you’re already using an exfoliant it may be overkill. Hard to generalise on this one and I reckon there’s a lot of misinformation, but broadly speaking most people can benefit from a Vitamin C!
Vitamin C is pretty much essential for protecting your skin during the day, it’s an antioxidant that protects your skin from environmental aggressors - stronger forms of Vitamin C can also act as exfoliants, so it’s always better to start off slow.
I tend to recommend the 12% that Christine linked above. The higher the concentration of C, the harder the texture is to work with (in my opinion!). Many Vitamin C serums are incredibly rich, and if you’re combination to oily you may find it hard to pick a Vitamin C that doesn’t leave you shiny haha!
I use the 23% on my arms actually - it is extremely concentrated to the point where it feels a bit gritty, however it’s very effective and I’ve been seeing results… personally I wouldn’t be able to use it on my face though. Between the exfoliation that I’m already getting elsewhere, and the protection that I can get using a less concentrated vitamin C, I’m happy with the 12% and that’s usually what I recommend except for people who are already regular users of C