T-Mobile works great, I’ve found them best Internationally. AT&T daily charges can quickly increase. YES, use as hot-spot. If chartering w Moorings base, they have option that work well.
Can you explain what you mean about AT&T? They have a flat $10/day fee as far as I know. I use it on Tortola with Flow and Anegada with Digicel and have always been charged $10/day.
Verizon is $10 a day as well. Works great on Anegada and while on charter last November.