For starters, you need a VPN that offers extensive support for upgrading your router with the DD-WRT firmware, either through web guides or customer support. Ideally, you also want OpenVPN support as it’s the most secure and configurable security protocol in use.
The VPN’s performance should be speedy and reliable, obviously enough, with plentiful server coverage always being a big plus point when it comes to finding a fast connection. And as ever, look for pertinent security and privacy features to keep your online presence secure and hidden from prying eyes.