Which is the one to go for?

I've got an A5 Octavia so the Micro CAN would work. But would it work with something like an A6 or similar? Or mkVI Golf?

Is a HEX+CAN likely to be more forwards compatible or just more backwards compatible?

Can a Micro CAN be used as a generic code reader on anything OBDII?

Cheers

The compatibility charts should answer that question...

http://www.ross-tech.net/VCDS/download/VCDSCompatibilityCharts.pdf

Even the latest VW Polo (6R) or the brand new Audi A1 (8X) do not work with the Micro-CAN hardware because there are still modules which require K-line communication. Something the Micro-CAN simply does not have.