Are they part of a five-eyes, nine-eyes or fourteen-eyes alliance? If yes, you may not want to be using that VPN provider, as those countries agreed to share information about its users in case of an opened litigation.
What is your budget – how much are you willing to pay per year? Perhaps for a lower price, you would be willing to make compromises.
Is the performance reported by users good? Have you read some reviews?.
Does the VPN provider officially support OPSense (or pfSense)? If not, are there guides available (on YouTube or blogs) where someone provides step-by-step instructions on how to set it up and troubleshoot it?.