there's no "best," only "right". That means there can be multiple options for you depending upon where you live along with other factors. Here's what you should look for apart from kill switch.
1.encryption and different modes of connection like IKEv2 and others
2. more servers
3. no connection timeout or in plain words, no drops
5. An IKS (or internet kill switch if you will) so the whole internet connection drops if your VPN connection starts acting. This will ensure no bytes are transmitted even if your VPN connection accidentally got down.
Before you do decide to settle for something, do read more on how torrents and vpn go together.