Most of the companies that sell to the public use the same manufacturers of LFP cells (Winston, CALB, Hi Power, GBS are a few). Price differences between the cells themselves are small and the quality is the same between them (at least I'm not aware of any that stand out). There's not that many available to the general public. The one's you read about you simply cannot buy, not to mention they are custom built and designed for specific environments. The company most used on the racing sailboats is Genasun, I think, and they seem to be accepted as the best BMS manufacturer also. Mastervolt is another. Both are really expensive and only sell pre-packaged batteries (cells plus BMS). I don't know what cells they actually use.
WinstonCALBGBS