There are some important factors to consider in choosing a VPN service provider. The following is a list of questions for you ask yourself or even ask the VPN host.

1. Which protocol to use?

Use the OpenVPN protocol. It’s more modern and easy to configure third party clients like Viscosity or Tunnel Blick using the configuration files the VPN Service Provider gives.

2. Can I do everything I normally do on the VPN?

You should consider routing all traffic to protect yourself. Ask the Service Provider if they block any ports, e.g. SSH, chat protocols?

3. What IP network do you usually connect with?

Ask them what their network and subnet is. E.g. 192.168.0.0/16, 172.16.0.0/12, or 10.0.0.0/8?

Ask yourself what your home network is, what networks your favorite cafés use, and what network your company VPN uses if you have such a connection.

4. IPv6

Do they route IPv6 traffic? If not, turn your local IPv6 address off. On OSX first list all network interfaces with:

networksetup -listallnetworkservices  

... then turn it off one by one:

networksetup -setv6off Wi-Fi  
networksetup -setv6off "USB Ethernet"  

Double check your address is being mapped to a location other than where you sit.

5. Traffic Logging

Make sure the VPN Service Provider does not log traffic of their customers. Ask them explicitly and read their privacy policy.

6. Payment

Do they accept month to month payment? If so, that’s low commitment and you can make sure it works with your connections rather than paying for a year up front.

7. Connection ports

Which ports do you connect to their VPN server with? E.g. TCP 80, 443, or something on UDP? You might get blocked on a company network depending on the outgoing port. Usually TCP 80 and 443 are free reign within corporate firewalls.

8. Hosts in multiple countries

Popping out of different countries might be something you care about - so definitely read through the Service Provider’s list of endpoints to see if it meets your needs.

9. Customer response time

Email support and test customer service response time. Do they respond in minutes, hours, or days?

10. TOR over VPN

If you use the TOR network, you would probably ask them explicitly if they support it.

11. Which country is the company based in?

Does the company’s country honor your government’s subpoenas for Internet traffic? Even if you’re not planning on breaking the law you’re better off basing your connection in a country who’s not a pushover.

12. Simultaneous connections

If you’re going to use the VPN service with multiple devices, which is quite common, you should ask the prospective VPN Service Provider if they allow multiple devices simultaneously.

13. Customer support PGP

Does customer support have PGP? If they do, they’re pretty serious and that should weigh in your decision.

14. Paid or unpaid service?

You should use a paid service. I used free ones for a long time and there is always a tradeoff. Either it’s not as reliable, slower, or there is a cap for traffic daily.