In terms of guardian, you can do arakaali's fang/Herald of purity. Mostly you either need to do unbelievable amounts of damage or be mostly immortal to do wave 30. Guardian can't really do the damage so you need to try and be as tanky as possible which means aegis aurora, chaos inoculation, divine shield, max block and so forth.

I do wave 30 on a cremation Necro for example because I can't really die due to 88 all res and aegis.