I think it's either Jane or Max.
I would like it to be a major character like Max, but could imagine it be Jane because she's always back and forth. They could just make her the killer so she can Bugger off once and for all.
There are loads of people who I would be underwhelmed with (Abi, Ben, Cindy, Lee & Jay). At least The Crokers would be a 'wtf' moment.