Hi Uhhidk Welcome!
What exactly do you mean by stay secure? Most all internet traffic is encrypted. A VPN moves trust from the ISP (Internet Service Provider) to the VPN provider. So the ISP will only see all your traffic going to the VPN provider. Since most web traffic is encrypted, the VPN provider will only be able to see which web site domains you are visiting, not specific pages or data entered on websites.
As far as cellular providers, I think in the US, Verizon is one of the better ones and AT&T is one of the worse ones. As far as the company's security practices, how long they keep logs etc...