Sadly I second everything that Blu has said. We put Dunraven 1st because it is our closest school (excluding a catholic school we would not have got into nor would have tried). My DS could walk there if he had too - he won't!!
We didn't get it. We got our 3rd preference school initially - a school farther away. I think 1500 applied for Dunraven last year.
We got a waiting list place. We were surprised and delighted but had really put it out of our minds and wholeheartedly embraced the allocated school.
We also put 2 schools down out of our six that we were fairly certain we would get a place at should all else fail. You really don't want to be in the position of not getting any of your six and then the borough allocating; you will be allocated a place after all the on time applications have been dealt with.
Kingsdale has a lottery but also music places too if that is your child's strength.
If your child is arty or has an aptitude for languages try Chestnut Grove. Outstanding co-ed in Balham. A few of my son's peers got in on language this year and 3 live outside what would be considered catchment. One lives in a Waddon, one lives in Norbury. Very easy on train - Thornton Heath to Balham 10 mins and school virtually on station's doorstep. They test in early Dec for arts/languages but you have to do a Wandsworth test too in November.
How are the Croydon schools? You don't mention any. I presume there is a Harris about? The ethos wasn't for us but I know loads of families who have happy children at them.
It's a horrible time and a rubbish process but you really have to look at the admission criteria for all the schools you are interested in and ask yourself "Do I meet it?" Otherwise you're just wasting preferences.
Good luck!