Polish OC? I don't think they are really all that powerful. At least not in the US.
In Europe there were the Pruszkow and Wolomin crime groups at the beginning of the 90s. Nowadays Polish OC is far from noticable.
Out of the crime groups you mentioned the Greeks in my opinion are the sneakiest of them all. You rarely hear something about them, but anywhere where a Greek immigrant neighborhood is located there's gambling- and drug-based (mainly meth, but also cocaine) organized crime.