Default [Q] Best VPN client for Android

Recently I purchased VPN service from Private Internet Access. I've been using their app to establish a VPN connection on my Nexus 4, however I find the app to be buggy and generally lacking. I was wondering what the best way to setup a VPN connection on Android is. I know that Android has a built-in VPN setting but it requires the use of a lock-screen password which I'd rather not use. If possible (and I'm not sure that it is) I'd like an app that can seamlessly switch between a Wi-Fi connection and a mobile data connection. Any tips/pointers are greatly appreciated!