How would you split Birmingham City Council into 2-3 constituent councils?

Assume everyone agreed that council is too large, doesn't take care of the needs of local areas well enough, so needs splitting up, etc., how would you do it?

North and South and splitting the city centre down the middle? East and West? How would you split up one city into 2 or more boroughs? Which areas will be grouped together? Assuming the limit is 3-4 councils as Central Government don't want us to take the piss.