The Serpent is the largest in diameter. Because of that you can get some problems to leave some flesh in the body, beside that, on some engines it will not fit because the main needle is to close to the air intake. Older Picco's like the G1 for sure has this problem.

Picco designed his own one, it is smaller and has less but larger holes inside compared to the Serpent. This seems to give a better airflow to the engine.
I believe the Nova box is the same size as the Picco.

The Mugen is compleetly different, it creates more noise and does give more air and so less drivetime but at this moment it is the only one fitting .12 engines.....