Sure, some reasons for Mullvad:

• If you go to their website, you'll see that your adblock blocked 0 items. Try getting the same result basically anywhere else, specially at other VPN websites.
• They don't require any details to create an account, your account is a number, similar to how you Bitcoin works.
• They are based in Sweden
• Their price is 5 euro a month with 10% discount if paid in Bitcoin. They don't run any scammy sales, or spam about their service.
• If you want to stop using them, you simply stop paying. Try cancelling some of the other VPNs, you'll have to click multiples times somewhere, and they will be trying everything they can to keep you inside. In fact, Mullvad recently stopped their subscription model as they want to store even less data about you: "We are removing the option to create new subscriptions"

And that doesn't even cover the tech part, which is one of the best in the market.