I have been using Mullvad since forever (actually recommended by the site of the article). They are extremely helpful, and are generally recommended in VPN reviews that do not have affiliates (including the site you linked to).
They do have both wireguard and openvpn options, as well as an app with a GUI (with support for both).
My favourite part is the support though. I got help with weird openvpn configs that didn't get answered in the openVPN forums for ages, within an hour.
+1 for Mullvad. Been using them since the beginning but never used their support so can't comment on that. One thing that bugged me was the general instability of Mullvad vs others, a few years ago connections would often drop or become extremely slow. For the last two years this seems to have been massively improved.
Connection dropping is one of the major issues with any commercial VPN provider. I recommend to create a script which runs openvpn and immediately after that "ip link eth0 down" to prevent leaks.
They do have both wireguard and openvpn options, as well as an app with a GUI (with support for both).
My favourite part is the support though. I got help with weird openvpn configs that didn't get answered in the openVPN forums for ages, within an hour.
I am a very very happy customer.