My mom has Verizon but she wants to change to a GSM carrier so I told her to switch to AT&T and I told her what she would gain from switching but she wasn't convinced enough so anybody got anything else I could tell her.
Before switching, she should check out the service where she would use it the most. Service is not guaranteed everywhere. Each provider has their good points and bad points. It is only a good deal if it works where she needs it most. Both providers are good otherwise they wouldn't be on the top. Sorry, that is not what you are looking for, but that is my honest answer.
This is a user to user forum. I am a user, just like almost everyone else on the site.
*The views and opinions expressed on this forum are purely my own. Any product claim, statistic, quote, or other representation about a product or service should be verified with the manufacturer, provider, or party.