Visiting my girlfriend, F or L visa?

I will be visiting my girlfriend this january (she's a Chinese national). Should I apply for a L type or an F type? An F type sounds very complicated however it seems to match my reason to travel to China. Will I need and invitation letter from my girlfriend? A L type seems more convenient to apply for (less paperwork) but I don't like breaking the rules. I know hostels usually register you at the local police station, but I will be staying at my girlfriend's place. Will I get in trouble if I don't register?