Short version: Use Streisand. Use Tor. Use Signal.
This mini-rant came on the heels of an interesting twitter discussion: https://twitter.com/kennwhite/status/591074055018582016
Provider / "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
UnblockVPN / xunblock4me
VPNReactor / VPNReactor
*Honorary mention in the VPN Hall of Shame, on general principle (for blatant sexism and utter insincerity): DoubleHop.me
Moral of the story: Don't believe everything you read on, say, TorrentFreak and PCMagazine. And (crucially) think about your threat model—are you guarding against amateur WiFi snoops at Starbucks or Marriott? Reducing identity monetization profiling by ISPs (ie ad tracking)? Minimizing exposure to government surveillance? Trying to be anonymous online? If the latter, a VPN won't help much.
Citations:
https://www.google.com/#q=goldenfrog+thisisourkey Archive: http://archive.is/qlrLK
http://www.gfwvpn.com/?q=node/224 Archive: http://archive.is/EdpFV
https://www.vpnreactor.com/android_l2tp_ipsec.html Archive: http://archive.is/uwJvk
http://unblockvpn.com/support/how-to-set-up-l2tp-on-the-android.html Archive: http://archive.is/4To5Y
http://www.ibvpn.com/billing/knowledgebase/34/Set-up-the-VPN-connection-on-Android-handsets.html Archive: http://archive.is/srptW
https://www.astrill.com/knowledge-base/50/L2TP-IPSec-PSK---How-to-configure-L2TP-IPSec-on-Android.html Archive:http://archive.is/PZpRU
http://billing.purevpn.com/knowledgebase.php?action=displayarticle&id=33 Archive: http://archive.is/R4JTi
https://www.privateinternetaccess.com/pages/client-support/ Archive: http://archive.is/U1bkL
http://torguard.net/knowledgebase.php?action=displayarticle&id=58 Archive: http://archive.is/iKJjl
https://www.ipvanish.com/visualguides/L2TP/Android/ Archive: http://imgur.com/IQU1mdg
http://www.earthvpn.com/android-l2tp-setup-guide/ Archive: http://archive.is/roKtf
https://nordvpn.com/tutorials/android/l2tpipsec/ (scroll down) Archive: http://archive.is/BQumt
*DoubleHop.me: Archive:http://archive.is/G11WQ and http://archive.is/MZgWE and http://imgur.com/Zn5HSIj
https://www.slickvpn.com/tutorials/ipsec-for-iphone/ and http://archive.is/h4rI9