with which characters do you have most sympathy for?

I think the most obvious character to feel pathos for would be Eva Smith. Eva is the girl who the Inspector claims worked for Birling and was fired, before working for Milwards and then being dismissed. After being abused by rich people, it is suggested she was sexually assaulted by Eric, she takes her life. You might consider Edna "The parlour maid." who reminds us of Eva.