Makro 120mm CFe or Makro 120mm CFi > Makro 120mm CF
Vary marginal but the CF is the oldest, the CFi &CFe has slightly better coating and the CFe has the electronic contacts.
So for a 503CW CFi would be your best option really the CFe was to provide metering on the 205/203 so isn't really needed but if you can pick either up for a reasonable price it won't make much difference to your images but I'd have thought the Fe would perhaps be more expensive??