If you’re talking about signal, it depends on where you live, as @filmfann said. I live in the Bay Area and Verizon was voted #1 for best signal/most service, ATT&T was #2.
I have Verizon and my mom has AT&T.. having used both services, I think I prefer the Verizon simply because I get a better signal most places, plus there have been times where I texted my mom and she never received the texts, so that makes me wonder what’s up with AT&T (I texted her from my Verizon phone and from a Tracfone).