The main value of choosing a national provider such as ATT is that there are local phone access numbers everywhere. This is in contrast to localized providers, most of whom do not have provisions for free phone access out of their current area. This means that if you travel, you will have to place a toll call to get your mail. Based on my experience with several providers, I prefer local ones because of the personalized service and response that they provide. Originally, I had expected performance to be better with large companies, but I found it not to be so.
Locals have a stake in their business, and they know that service is important.
An experienced user can by-pass it, but it is valuable if you are new at it. Recently there have been a number of ads offering very low prices if you prepay for a year or two. Reports on these have not been encouraging, as with your money in hand, there is little incentive for them to improve their service. Your best bet is not to make long term commitments. The biggest problem is that when you change providers, you have to notify all your contacts about your new e-mail address.