Personally - 3
I don't know how you blokes with 6,7,8 +++ can get used to them all and know how to get the best out of them.
I prefer to have boards that are suited to a wider range of conditions. I find it hard to transition from board to board - turns me all gumby 
Depends on how often you surf,conditions play a large part of that and what you want to get out of your session.
So for me its three.One for micro small,one allrounder for the fatter days and one for low to mid tide fun.
Micro = redline 9.6 x 23 x 3 1/8 could even go more volume
Fat = fireball 9.6 x 23 x 3 could go down on length
Low tide = ufo 9.3 x 23 x 3 love that board
I always look at what I want to get out of each surf and select the board or sometimes boards to whack on the car.
Travel quiver is three boards - Big shorty and two guns will do all conditions up to about 10 foot after that my schfincter says no....at home the quiver is ever expanding once I find one shape I like I try to get another similar in case the first one ****s out then I will go of on a tangent and get the same bottom contours with different dimensions etc etc....currently running :
1 x 5'4 Fish
1 x 6'6 Egg single
1 x 1970's single
1 x 6'6 short board
1 x 7'0 Short board
1 x 7'6 Indo gun
1 x 9'4 HP Mal
1 x 9'6 SUP
1 x 11'6 SUP
1 x 12' SUP
The 6'6 short board is a cracker and has been the template for the 7'0 and the 6'6 single.....
i'm thinking on the same lines as mac for those 3 different surf conditions except i'd use an old mal for those waist high and under sessions.
I have 2 longboards at the moment with another on the way.
10' cruiser
9'1 thinned out high performance longboard
9'4 is coming in about 5 weeks and I'm getting that as something in between that I can put into the car and ride in any conditions.
As far as longboards go I reckon that should cover it.
I've got an 8'shortboard shape for good waves and two 7'6 eggs one a thruster and the other a quad and a 6'10 shortboard.
I also have a 4'8 glass bellyboard that I drag out every now and then. Its heaps of fun to ride.
How I love polished resin 
At the moment I have 1 x 9ft sup/ 1 x hp 8.0 mal and a 9.6 semi-log.
Once the new longboard shop opens on the goldy in the very near future my quiver may change as regularly as I change my undies - at least every 3 months
Sorry - my ultimate quiver would probably be a 9.4ish longboard and a 9.6ish sup.
Find the photo of Simondo's quiver and thats your answer! A board for everywhere you surf in different conditions would be the most direct answer I reckon? I dont have a quiver but thats how I would want it to be If I had the $$.
1 x short board 6'10"
1 x hull, fish or mini simons 6'10"
2 x HP Longboards 9'4"-9'6"
1 x Semi log 9'7"-9'8"
So 5, need to sell a couple well 1
6'3" semi fish
6'8" little gun
7'6" hybrid
8'0" mini mal
9'6" redline
5'10" short kite board
6'0" gun kite board
6"8" SUP
