In the US, ATT + VZW = generally good service everywhere

If you preferent results to excuses, you get a dual sim phone and use whichever line has the most bars (I keep a Tmobile 5G access point for my computer stuff)

Yes, I do know that is a hardware thing, but I am pretty sure you already connect to more than 2 towers at the same time, even with a single sim. As for, what is the point of more than 2 at the same time. There are already plenty of people who use 2 sims to, for example, separate work and personal life, or personal stuff, and stuff like microsofts stupid 2 factor. Also, when traveling, it would be great to be able to add more sims, without disconnecting your previous sims, which may be connected to subscriptions which you might want to keep running, though, to be honest, I don't know much about how stuff like that works with esims. Even if you could only have 1 or 2 active at the same time, lots of esims you can switch on or off would be great. Also, having a bunch of burner prepaid sims which you can turn on and off is really nice.