If this is your first module that you are building, I would suggest you go with v3.3A. v4.1 and v4.2 have some components (SMD ATmega328, resonators, FTDI chip) that might be really hard to solder for a first timer.
The downside of v3.3A is that it lacks the code upload via USB capability, so you would need a FTDI cable for that. On the good side - on v3.3A the ATmega328 can be easily removed and reprogrammed (bootloader/code uploads) using a Arduino Uno board.
2001 9-5 SE V6; 2006 9-5 Wagon; iOS; BlueSaab version = "latest and greatest" :)