I see the Gallentean and Caldari militias as being a lot more organized then the Minmatar and Amarr ones.
For the Caldari, the militia acts like the private army of the unified people, something that goes past corporate authority and such, and is thus directly controlled by the politicians. Its left with a lot of autonomy, but I could easily see the militia turning on a caldari corp if it strayed from the group.
For the Gallenteans, they're basically an extension of the Gallentean Military, a separate branch of it, a loose branch in a lot of senses, but still sort of military. They probably treat capsuleers as paramilitary contractors do take care of things they don't want to take credit for, and thus, they don't care who they're paying, as long as the work gets done.
The Amarrian militia is more like well, its a crusade. The 24th one. The Empress raised a flag, declared crusade, and is giving a rubber stamp and lots of resources to anyone willing to fight for the cause, and they're not too particular about who is fighting. Its really a lot like the Christian crusades, just transplanted into the eve universe. There's a lot of bad people in the 24th IC, but as long as they're doing Gods Work, its all right.
The minmatar militia, is probably the closest thing to a real militia. Its not terribly organized, its not full of nice people, their training is a very mixed bag, but these are desperate times, and the people must be rallied. If you can fight the Amarrians, anything else about you is overlooked.