Mullvad is good and they do run promotions sometimes but unfortunately they are within the 14 eye countries group so weight it accordingly. NordVPN is great too and they do run promotions all the time, dump their client and use OpenVPN.
The following considerations will help you getting the best service among such huge numbers of VPN Providers:
1) Data logging policies and Jurisdiction:
it is important to find providers with minimum logging policies as it's the only way against modern surveillance technology. Also try to find a companies that installed their servers out of the uS, otherwise it is easy for US government to access your data.
2) Level of Encryption:
Before you subscribe to a VPN service, you need to ensure that it provides adequate security for your web sessions so look for a company that offer higher levels of encryption as if 128-bit encryption can’t be cracked by brute force, 256-bit encryption is 2^128 harder than that.
3) Diversity of servers and locations:
It helps you to find a server with lower latency and higher bandwidth.
4) Customer service:
A good customer service is generally indicative of the capability of the company especially if they take criticism and complaints in a positive manner.
5) Device Compatibility:
good provider should offer support for all major desktop as well as Mobile operating system. your smartphone is almost as powerful as a laptop these days, so make sure that your VPN is usable on your device also you may need to verify that your provider supports Boxee, XBox or DD-WRT router or....
6) Price VS services:
compare prices, and make sure you get the best deal available, not just the cheapest. All providers offer certain advantages and drawbacks, so consider carefully before committing.