Is there any reasons to use one over the other, and vice-versa? And how will OP know which one they should use first?
Oops, I forgot to specify, I'll add here.
ESET: Very light antivirus, excellent detection rate, excellent protection against PUPs (one of the few to block them).
It doesn't have VPN or other features (you can have more options like safes in Smart Security, but it's very expensive).
F-Secure: Antivirus also very light, excellent detection rate too. On the other hand, it's all-in-one (Internet Security has a relatively good VPN, while Total adds a password manager, and you can use Bitwarden, which is free). F-Secure is bad on PUPs.
All in all, these are 2 good, lightweight antivirus products. The choice will depend on whether you want a program that will protect you (and if you don't need a VPN) or whether you want a suite that includes everything (antivirus, password manager, VPN, etc.).