ICloud private relay is a VPN provider, but if you are talking about choosing between Apple and others, I would suggest you try out Proton VPN (freemium, limited free speed), Windscribe (freemium, data cap on free), Mullvad (paid) or IVPN (paid) + you can use Tor if you don’t care about speed (although many websites block tor users)
As for if you shoud you use a VPN 24/7? As always, it depends. A VPN protects the IP addresses (and often domain names) of websites you visit from your ISP (but the VPN provider can see them). This can be useful for cencorship circumvention, as the ISP could ban certain IPs from being acceses (which also includes the IPs of VPN servers). The only thing the ISP sees, is that you are connecting to some IP (the VPN server’s IP).
A VPN also protects yout IP address (which often contains location information) from the websites you visit. This is useful to circumvent geo-blocking by websites.
In short, you should use a VPN if you want to hide the websites you visiting from your ISP (but let the VPN provider see them), or want to hide your approximate location from websites. Usually VPN providers want you to use them constantly, as you pay more if you do that.