T-mobile, because I got some plan years ago that gave me true unlimited data instead of "unlimited", and I don't want to try to find another plan with that.
My plan has like 10GB or so of tethered data, which pro-tip, you can get around by adjusting the TTL of packets sent by devices connected to your phone so that they appear to be coming from your phone. N.B. that t-mobile doesn't like this and may cut your service off.