You need both, but for different reasons.
Aftershave isn't really a bleeding-stopper — it's an antiseptic with some mild astringent properties from the alcohol. It'll slow a small bleed, but it won't close a cut quickly.
Styptic powder is the targeted closer. Use it first on the nick, wait 30 seconds, then proceed with your normal aftershave routine.
The order: Rinse → Styptic on any nicks → Wait 30 seconds → Aftershave / balm → Moisturizer (optional). Don't reverse the order — aftershave first will dilute the styptic.