The family plan actually seems like a lot better deal.
The family plan has no free calls to Canada / Mexico, and neither does it have no-roaming unlimited service in Canada or Mexico. I've just had to make a business trip to Canada, and I had to get the T-Mobile's One plan. I made a family vacation out of the business trip, so I got two lines from T-Mobile for $100 with unlimited calling, texting, and data (up to 28 GB) as well as 10 GB of tethering. The tethering really saved my bacon as in the most crucial moment, I couldn't VPN via the corporate network to the network devices from Canada. So, I used the T-Mobile's tethering and was able to achieve everything I needed. The project turned out to be a success.
T-Mobile really surprised me. In Ontario, they partner with Bell and Telus. I actually had a choice of which provider to choose manually, or I could set it to automatic and let my cell phone choose the provider. I was blown away by the speeds of data in Canada. I was consistently getting close to 100 Mbps down and over 20 Mbps up. On many an occasion, my download speed was over 100 Mbps and my upload speed was over 30 Mbps, and that is from within concrete office buildings as well as on the street. The fact that I was able to get all of this for $100 also blew me away.
Now that I'm back in the US, I'm using the bandwidth meter app (Ookla) on my iPhone 7 as well as on my wife's iPhone 6s Plus and measuring bandwidth everywhere I go. I am getting amazing speeds on T-Mobile in the US. From my house, I get over 100 Mbps down and over 30 Mbps up on T-Mobile LTE. I go on a forest trail for a 4-mile walk and get over 60 Mbps down and about 20 Mbps up. I popped in the AT&T SIM (family share plan) in to my iPhone 7 on the same forest trail, and the bandwidth I got from the same spot was 6 Mbps down by 1.2 Mbps up. Currently, I have 30 MB of data on my family share plan (I jumped on every promotion AT&T had in the past few years to upgrade my data allowance), and this 30 MB of data includes tethering.
I have two more weeks left in my AT&T billing cycle, and I'm now seriously considering switching to T-Mobile especially with the T-Mobile One plan costing $100 for two lines for unlimited (up to 28 GB) data as well as unlimited voice and texting and 10 Mbps of 4G LTE tethered data. If I need more tethered data, I can upgrade to T-Mobile One Plus plan that gives me up to 28 GB of tethered data (same amount as on-device data) before T-Mobile would start throttling me, which is only 2 GB of data a month less than what I have with AT&T, but the 28 GB of tethered data with T-Mobile is per line (not shared). I believe T-Mobile One Plus costs $25 more per line, but my wife won't need it. So, even with T-Mobile One Plus at $125 per two lines (with the other line being on T-Mobile One), I'm still much better off with T-Mobile than these AT&T plans, especially considering that the $125 price is all inclusive (no additional fees or taxes). Additionally, if I want to travel, T-Mobile has free voice and texting in something like 140 countries, which is really unbelievable. In all foreign countries besides Canada and Mexico, T-Mobile doesn't have LTE data speeds, but they still provide unlimited data on 2G, which is better than nothing, and it costs nothing additional even though you may be half the way across the world.
I always thought T-Mobile was a crappy carrier, but the last two weeks made a believer out of me, and I now think T-Mobile has made an unbelievable comeback and is definitely worth considering switching to from AT&T or Verizon.