My first thought was "God the PRICE!!"
Assuming you know all that if you are thinking of state at primary and secondary, best bet is north-east sector of city - good (but large) primaries and then in good position for Beaumont, Sandringham, STAGS, Verulam. But of course the admission rules vary form year to year and popularity of schools vary from year to year. So don't plot your child's education - but living in NE does generally put you in better position.
I disagree about City Centre - I live there and no trouble at all. Totally shit for school choice though
Madeindevon - actually I'm in favour of the curretn lottery system because it means those of us in centre or south can then stand a chance of getting into STAGS or Verulam - v. v/ difficult otherwise.
St Columbas - yes it's boys and catholic, but in practice accepts a very side range of faiths. Lots of muslims & hindus there. Excellent pastoral care, but not in same academic league as St Albans boys school.
Garden Fields excellent - not sure about how easy to get in though. Aboyne Lodge - not a hope in hell. I know of someone in the same road who could not get their child in there this year because of the sibling issue.
Highfield Park ... well there is a reason why it's more affordable and that's because of the schools. The nearest secondary is FB which is in special measures. Some kids from Highfield have got in at Beaumont, but that varies tremendously from year to year.