Ill do either. Criminal sounds more fun but i like the sound of an enforer.
The differences are purely cosmetic except for these:
The enforcers get to choose what to do and when, based on how other enforcers (and pedestrian A.I.) report crimes. The payouts are larger (and reporting crimes allows you to get more experience than a similar criminal run) but it takes a bit longer to get a payout.
The criminals can fight each other, and do not get to choose what to do and when. The payouts are smaller, but are obtained more often.
There are also, other minor, differences, such as criminals get to raise their prestige level by killing pedestrians/running over signs, but if an enforcer does the same their prestige level is lowered. An enforce can only raise their prestige by completing objectives and killing criminals. This acts as a kind of balance against the extra experience earned by the ability to report crimes.
There are pros and cons for each, but in the end it doesn't really matter. The only thing that bothered me was
I hated not being able to take a break between missions and restock on ammo and such. As a criminal, you constantly get APB'd and you never have the option to stop attracting heat.
so I'd go with enforcer every time.