The term 废物 is the one I hear the most. Someone else said they think it's northern slang, but my friends are all Taiwanese and they use this word all the time. So I think Chinese speakers everywhere use it. People can use it in a joking way with friends or they can use it like an insult. You can also use it to refer to yourself. For example 我最近都在家里当废物
If you want a less slang way to express something close to the meaning of loser you can use the term 没出息, it literally translates to 'no prospects', but it's basically like calling someone a loser. I watch a tv series where the main character works in a drinks shop and his family always tell him 你没出息. I think this is a term that is OK for written language
Also I used to read a lot online about the term 吊丝. It must be a term that is most,y used in mainland China because I have never heard my Taiwanese friends use it. Apparently it also means loser, but some people use it to refer to themselves. My impression is that it's similar to a youth subculture, but I'm not qualified to explain it really
I'm not a native speaker, but I hope my answer is helpful taken in conjunction with the other answers.