To be honest, none at all. Don't fall prey to any delusions and believe that joining a resistance force was actually a good idea to increase your chances of survival if you joined before late 1944. They were not effective and the effect on the overall war was minuscule compared to the risk you would be exposed.
Contrary to popular opinion, German counterintelligence was pretty effective. The entire French resistance from 1942 to 44 was full of German double agents and their communications were read by German occupations forces.
Soviet partisans idem? Their radio discipline was abysmal and the Germans had broken your codes with ease. So, if you tried to any mayor attack, the possibility was high that you would run into a German ambush.
Polish resistance? They did better, but good luck surviving the uprising and the Soviets afterwards.
German resistance? Don't try it, just don't try it. The SD will find you.
Greek resistance? Maybe one of the better choices, but they more occupied with fighting themselves rather than the Nazis. Greek royalists against Greek communists.
Italian resistance? Largely irrelevant.
Yugoslavian partisans? Well, that will be one of the most interesting fronts of WW2, not to say chaotic. Albanians, Bosniaks, Croats, Germans and many others that hate you vs you and the Serbs. And I can promise you that you as a resistance fighter don't want to fall into the hands of the Handschar. Very friendly people.
