my take on the poster's question is that they are looking for a commercial VPN service and not a local VPN server on their OMV.
Sorry that I can't be more helpful but my answer is that I don't know which is the best value/performance VPN service. I would try googling 'best VPN service' and have a look at the prices and performance/restrictions. You will probably find some that have a free trial and this will be a good way to find a good one.
I have been to various sites like these talking and reviewing about the best vpn services available, but somehow i don't believe them i feel these are not actual user reviews.