Wouldn’t it be great if there were only a few, standardized, alternatives when choosing class? We agree. However, the train operators themselves choose what they call their different class options, which means they tend to be called things like "Sparpreis", "Super Flex Premium" and sometimes just "Seat". This is not ideal and we are working actively to standardize how ticket options are listed in our service.
Which option you choose to travel with is entirely up to you. The more expensive options usually mean better comfort. If you feel unsure about what applies to each class option, you can check it out on the train operators' websites, or in their terms and conditions.