My order would be something like this:
Sydney - Love their defence, they rebound and intercept opposition marks with monotonous regularity. They really work together as a unit and they have a lot of versatile players that can play one on one, zone off and rebound going the other way.
Collingwood - Underrated a bit because Brown/Tarrant/Reid are never fit at the same time. But at full strength with their very talented rebounding smalls, in particular Shaw they have a formidable defence.
Geelong - No longer the No1 (imo) but still a quality and experienced defence. Their 3 talls in Taylor/Scarlett and Lonnergan are terrific. Their smalls aren't quite as good, Enright has been a gun for many years but he's definitely slowed down this year, guys like Hunt/Guthrie are decent but not amongst the elite. I think they have a slight vulnerablity against quick small forwards as a whole.
West Coast - Led by the always consistent Glass and the underrated Mckenzie they always are hard for talls to play against. Waters has become elite this year and Hurn gives good rebound. Selwood is a solid citizen and same with the likes of Brown and Schofield. Nothing wrong with this defence at all, could easily be 2nd.
Essendon - I've slotted us in at 5th, pretty solid, well balanced unit. Talls of Fletcher/Hooker/Carlisle (nice talent here)/Pears. Then the smaller defenders in Hibberd/Hardingham/Dempsey/Dyson/Heppell etc. Been a pretty good defense this year, has held together consistently only conceding more than 80 points on a couple of occasions. A lot of good rebounders too.
I'll stop the list here but I probably would have had Adelaide/St.Kilda/Hawthorn as my next 3.