What you want to see in a VPN provider is:
lots of different servers to choose from
dedicated servers (vs. VPS servers)
a no-logging pledge
how to stay anonymous:
Pay with a "cash card" or in BitCoin (or other untraceable funds)
Change servers frequently - once a week is usually enough
Ensure that your DNS searches are private - not just your p2p! (Personally, I keep the entire system behind the VPN!)
To what some people are claiming about ports and open/forwarding: if you use an advanced server that actually overtly supports p2p (like NordVPN), you don't need to worry about this... they can see the port you advertise in your client, and they will forward it over your VPN link (and yes, that means you DO NOT need to open the port on your local router!)