Best Carrier Options in the U.S

After doing a decent amount of searching for what Carriers the Librem 5 will support the best, I have become confused as to what Carrier is the best option for the Librem 5 in the United States. If someone could point me in the right direction to figuring this information out, that would be great. Also, does anyone know what modem the Librem 5 will have, or is that yet to be announced? Thanks.