Don't ever trust VPNs and here is why....
1) Not using a VPN or rolling your own is probably best. See here (and avoid the list of dodgy VPNs):
Short version: I strongly do not recommend using any of these providers. You are, of course, free to use whatever you like. My TL;DR advice: Roll your own and use Algo or Streisand. For messaging & voice, use Signal. For increasing anonymity, use Tor Browser for desktop, and Onion Browser for mobile.
This mini-rant came on the heels of an interesting twitter discussion: https://twitter.com/kennwhite/status/591074055018582016
Again I strongly do not recommend using any of these providers.
Provider / known "Secret" Key
Astril / way2stars
EarthVPN / earthvpn
GFwVPN / gfwvpn
GoldenFrog / thisisourkey
IBVPN / ibVPNsharedPSK!
IPVanish / ipvanish
NordVPN / nordvpn
PrivateInternetAccess (PIA) / mysafety
PureVPN / 12345678
SlickVPN / gogoVPN
TorGuard / torguard
TigerVPN / tigerVPN
UnblockVPN / xunblock4me
VPNReactor / VPNReactor
Yes, I know. Many/most of these offer OpenVPN, or special clients for IPSec. But for all of the above, they are actively placing a significant portion of their user base (particularly those with older Androids and desktops) at risk by not using per-user PSKs. If your threat model is streaming BBC or helping your cousin geo-shift Hulu, go wild and plug into the Mad Max-esque Thunderdome commons and take your chances. If you're a dissident in Tehran or Riyadh, be extremely cautious of any of these providers.
2) This is why you shouldn't trust VPN providers in general and why the VPN bottleneck is asking to be pwned (it is a glorified proxy and simply a money spinner).
Trust in them is misplaced (plus most of them are in "Fourteen Eyes" countries anyway):
Because a VPN in this sense is just a glorified proxy. The VPN provider can see all your traffic, and do with it what they want - including logging.
But my provider doesn't log!
There is no way for you to verify that, and of course this is what a malicious VPN provider would claim as well. In short: the only safe assumption is that every VPN provider logs.
And remember that it is in a VPN provider's best interest to log their users - it lets them deflect blame to the customer, if they ever were to get into legal trouble. The $10/month that you're paying for your VPN service doesn't even pay for the lawyer's coffee, so expect them to hand you over.
But a provider would lose business if they did that!
I'll believe that when HideMyAss goes out of business. They gave up their users years ago, and this was widely publicized. The reality is that most of their customers will either not care or not even be aware of it.
But I pay anonymously, using Bitcoin/PaysafeCard/Cash/drugs!
Doesn't matter. You're still connecting to their service from your own IP, and they can log that.
But I want more security!
VPNs don't provide security. They are just a glorified proxy.
But I want more privacy!
VPNs don't provide privacy, with a few exceptions (detailed below). They are just a proxy. If somebody wants to tap your connection, they can still do so - they just have to do so at a different point (ie. when your traffic leaves the VPN server).
But I want more encryption!
Use SSL/TLS and HTTPS (for centralized services), or end-to-end encryption (for social or P2P applications). VPNs can't magically encrypt your traffic - it's simply not technically possible. If the endpoint expects plaintext, there is nothing you can do about that.
When using a VPN, the only encrypted part of the connection is from you to the VPN provider. From the VPN provider onwards, it is the same as it would have been without a VPN. And remember, the VPN provider can see and mess with all your traffic.
But I want to confuse trackers by sharing an IP address!
Your IP address is a largely irrelevant metric in modern tracking systems. Marketers have gotten wise to these kind of tactics, and combined with increased adoption of CGNAT and an ever-increasing amount of devices per household, it just isn't a reliable data point anymore.
Marketers will almost always use some kind of other metric to identify and distinguish you. That can be anything from a useragent to a fingerprinting profile. A VPN cannot prevent this.
So why do VPN services exist? Surely they must serve some purpose?
Because it's easy money. You just set up OpenVPN on a few servers, and essentially start reselling bandwidth with a markup. You can make every promise in the world, because nobody can verify them. You don't even have to know what you're doing, because again, nobody can verify what you say. It is 100% snake-oil.
So yes, VPN services do serve a purpose - it's just one that benefits the provider, not you.
3) Don't exclude specific nodes in the Tor network - it goes against Tor Project advice and probably makes you less anonymous. Disregard this advice at your own peril.
Users can manually choose an entry or exit point in the Tor network,  but the best security relies on leaving the route (path) selection to Tor. Overriding the choice of Tor entry and/or Tor exit relays can degrade anonymity in ways that are not well understood. Therefore, Tor over Tor configurations are strongly discouraged.