Originally Posted by: Andrew at Tanks HQ 
This number is based on loads of factors, like all the other stats in the game there is a complex formula that goes into figuring out what their final numbers are.
For Initiative, most of what goes into this number is equipment based, how fast is the tank, how fast does the turret rotate, how much viability does the tank have, is it opened top, how many men operate the turret, how many operate the tank and much more fiddly bits.
Phil Yates has a spreadsheet he has created over the years that has loads of factors added into it, and we used that spreadsheet to generate this number. The number basically comes down to the tanks ability to react during a fight, so anything that would effect this gets factored in.
So to make a long answer a bit shorter, this is not an easy question to answer because it's not a simple formula that creates this number.
The quality of crew does not play a part, as each tank is considered to have an average crew. It is the crew cards you add that indicates an above average crew.
Hopes this clears some things up.
-Andrew
Andrew, first thank you for taking the time to respond to my post because this does help and is very useful. This at least confirms my suspicion that all the tank cards are considered to have average crews, and that the initiative rating is based off the characteristics of the tank.
I agree that this is not an easy question to answer because "it's not a simple formula that creates this number." However, it would be interesting to see how in detail the initiative ratings for both the Sherman (75mm) and Panther was determined. Using some of the details you mentioned above, it would seem that the Sherman (75mm) should have had a higher rating than the Panther. For example, equipment based:
Turret rotation speed - The Sherman is much faster than the Panther.
Turret space for crew - Both are about the same (not cramped compared to others).
Tank's Speed - The Sherman is slightly better than the Panther.
Battlefield Reliability - The Sherman is much better than the Panther.
Normal cross county mobility - Both are the same.
Road or hard ground mobility - Sherman is better because of tracks, see "tracks" below.
Ground Pressure - The Panther is better than the Sherman.
Visibility when buttoned - both are the same, both very poor visibility.
Visibility when unbottoned - both are the same if crew quality are equal.
Number of crew - both are the same.
Crew layout - both are the same.
Crew in turret - both are the same.
Crew communication with each other - both are the same (good compared to others).
Crew comfort - Both are about the same (good compared to others).
Rate of fire - The Sherman has a higher ROF than the Panther.
Gun stability - No contest Sherman wins. "Gung Ho" handles this (Gun Stabilizer).
Main Gun optics - German optics was better, and this applies to all tanks.
Acceleration ability - The Sherman is better than the Panther.
Braking ability - both are about the same.
Turning ability - The Sherman is better.
Suspension - The Panther is better.
Handling (driving) - The Sherman is better.
Turning (driving) - The Sherman is better.
Size - The Sherman is smaller (target acquisition).
Weight - The Sherman is lighter.
Internal equipment layout - For ease of use, both are about the same.
Radio Equipment - Both have radios - helps with communication and battlefield awareness.
Tracks - The Sherman's rubber blocked tracks have several advantages over the Panther's all steel tracks.
There are a few other little tank characteristics we can take a look at, but in most cases (not all) the Sherman is better than the Panther. So, using some of the major characteristics of the two tanks like turret speed and whatnot, it would seem that the Sherman (75mm) should have had a higher rating than the Panther.