I’m not going to lie, I download a lot of pirated content (especially anime) and I need to skip the limit that MEGA imposes on their downloads, so I need a free VPN that doesn’t affect so much the download speed since my connection varies between 500-800kb/s since I live in a Latin American shithole, I don’t care about the security or privacy issues that the VPN may have, haha. I tried ProtonVPN but the connection looks very limited. Thank you very much.
Server time and internet bandwidth cost $ so if someone’s offering something for free you’re the product 
That said, windscribe VPN is well-regarded and their free service has a 10GB per month cap, their paid services have no bandwidth limit. Just be sure to bind your torrent client to your VPN adapter so things don’t leak.
Good luck -
edit: I use Mullvad and would highly recommend them but they’re not free - 5€ a month.