Swerve drive 4, 2+2?

[kirtar]

Recently, I've been looking into omnidirectional drive systems (as defined in the whitepapers by Ian Mackenzie). It seems that my team is leaning toward prototyping a crab/swerve drive for next year.

There seems to be disagreement in terminology in this area, as some consider swerve as a subset of crab and vice versa. As clarification, I consider crab drive to steer all 4 wheels dependently, keeping them all at same angle (often by running one chain around the whole thing). I consider swerve to be a case where either all four wheels turn independently of each other or when two pairs of whells turn independently of the other pair.

As this has come around, I have a few questions:

1) On a 2+2 Configuration, is it usually arranged front/back, left/right, or does it really not matter?
2) Are there advantages in terms of performance of a crab as compared to a swerve and vice versa (except weight and complexity of building and programming)?