Two of the most-searched ingredients in skincare, constantly compared, and the honest answer is that most people would be fine with one.
What each is for
Vitamin C is an antioxidant. It's used for the appearance of brightness and a more even-looking tone. It's generally well tolerated, works in the morning, and is easy to add to a routine.
Retinol is a vitamin A derivative that affects skin cell turnover. It's the more powerful of the two and the more demanding. It goes on at night, it needs building up slowly, and it commonly causes dryness and flaking in the first few weeks.
Different jobs. Not really competitors.
Which to start with
If you've never used either, start with vitamin C. It's gentler, the adjustment period is shorter, and you'll find out how your skin handles an active without a fortnight of peeling.
If you've used vitamin C happily for six months and want to go further, retinol is the logical next step.
Using both
You can. The standard approach is vitamin C in the morning, retinol at night, which keeps them separated and puts each where it works best.
What you shouldn't do is start both in the same week. If something irritates, you won't know which one, and you'll probably abandon both.
The retinol warning that matters here
Retinol increases sensitivity to sunlight. In Australia that's not a footnote.
If you're using retinol and you're not diligent about sun protection, you're doing something actively counterproductive. That's not a marketing line, it's the reason retinol is a night product in the first place.
Give it three months
Both take time. The first month of retinol in particular often looks worse rather than better while your skin adjusts, which is when most people quit.
Whichever you choose, pick one, use it consistently, take a photo at the start, and don't judge it until autumn.
And if you'd rather do neither
That's a legitimate routine too. Cleanse gently, moisturise, protect from UV. Someone doing those three things properly is ahead of most people with a shelf full of actives.
General information, not personal advice. If you're pregnant or breastfeeding, retinoids are a conversation for your doctor.
