The only major difference is that the very first ones had a Delta fan that had some issues with noise and with magnets (the dbrand case's magnetic stand made the fan rev out of control).
There’s still basically one with a couple storage options - they have shipped with different fans though. My (fairly recent) unit has very reasonable fan noise.
There's variants with slight differences in hardware like fan and SSD. It's common for consoles too.
Ah yep, I'd definitely go for the highest end model. But I'd love it if I get the latest batch with better fans and such.
They switched suppliers for the fan, apparently their previous one was much worse and the fans were much louder and annoying.