For myself, AT&T has been my provider from the start in 2002. At that time, I looked on the internet for which carrier gave the widest range coverage throughout the U.S. and Canada. They had the largest number of places/areas. There's also was best for reception in areas I tended to be most.
They were AT&T and then Cingular and now back to the AT&T name. During medical excursions I was able to use their rollover minutes too! (all the free time in medical spaces leads to boredom). In 18 years, maybe 10 total dropped calls.
When I went to Smartphone territory, I found a decent plan with them as well. With Wi-Fi secure at home, it doesn't need a huge plan and Wi-Fi is available most places now(although not as secure, so use it wisely...do not put in banking info or other identity theft items).
Have used Samsung smartphones and been quite content. My first was a Galaxy 4 in 2012. One battery upgrade, it still runs well (even after it nearly drowned). Use it for Netflix and YouTube along with moderate internet stuff daily. Usually while its followup phone is recharging. The followup phone is the Galaxy 7 from about November 2016. Still top notch.
If you text, I have no idea what is the best plan. I have never texted and even though AT&T gave me free texting, I asked them to shut it off.
Samsung cameras on the phones seem good. I'm not a good judge on visual stuff, but the photos are clear. Additionally, I've done some ZOOM meetings and the image matters are good.