The provider they choose depends on data volume requirements and signal strength (speed) from local masts.
I only know about Three wrt ease of setup, where it was literally a case of inserting the SIM that came with the router, plugging in and turning on the router, then waiting a while as what was a TR-069 or similar did its thing. Three like to configure SIMs even for phones with several downloads.
If there is only one person in the household, then just upgrading their phone SIM for the amount of data could be adequate. Assuming their phone is 4G capable
. Tether the computer and maybe a tablet to it. That's what I did until I needed broadband for a cloud-updating 24/7 security camera setup, as obviously when the phone went out with me the cameras became useless.
(I think there are now some security cameras that have internet connection built in, needing a SIM in them of course. Which for more than one would be uneconomic when a router can handle several).
Remember also that any setup like this is useless for gaming, due to the latency being all over the place.
A good tip is to get £1 PAYG SIMs for EE, Three, Vodafone from a newspaper shop and load a tenner onto each, assuming they have a 4G-capable smart-phone. Try them all out for a few minutes at a few times of day and at weekends. EE will probably come out the winner on performance. Three could be perfectly acceptable, as it is for me, and cheapest.
My broadband basic info/help site - www.robertos.me.uk.
Domains, site and mail hosting - Tsohost
Connection - Three 4G, tbb tests normally 35-45Mpbs down, 65Mbps off-peak, 9-24 up.
"Democracy means simply the bludgeoning of the people by the people for the people." Oscar Wilde