U.S. Cellular

As good as it gets (for a wireless provider at least). I would recommend the Wacker location and asking for Marissa. I also recommend making an appointment in advance if you don’t want to wait an hour to see a sales consultant.
As for why I recommend this store: Coming from a horrendous customer service experience with Verizon, I wasn’t expecting much from US Cellular. I switched to get a lower priced monthly plan but didn’t expect more than that. I have been pleasantly surprised since making the switch. It’s not that everything has been 100% smooth (it hasn’t been) but the big difference is that the sales and customer service staff at my local US Cellular have actually been able to address issues and resolve them WITHOUT me spending endless hours on the phone trying to explain things to an 800-​number support person.
Maybe my expectations are just that low but with Verizon, any time I had a problem I would be told one thing by one rep, only to wait several weeks for what they told me not to happen. I would have to call up again, start over with a new person, and hope that the story they were telling me would be true. It never was.
I am completely astounded by US Cellular in the sense that even though things have been bumpy with my transition from Verizon and everything didn’t go exactly as promised, there has always been a real person ready to take ownership of the problem and find a solution. If it can’t all go right then this is the next best thing.