I've used Tracfone, Virgin Mobile, Ting, TPO, and a couple that are no longer in business. I'm currently with Cricket which is owned by AT&T.
If T Mobile service is good in your area take a look at TPO. They have low prices, and good customer service. Plus you can select a charity to receive 5% of your monthly fees. I chose American Family Association, but NRA ILA is also on the list. The only reason I left them is that T Mo has no coverage in a couple of areas that I travel to on a semi regular basis whereas AT&T does have service there.