VAs are what you make of them and each one is run slightly different and range from those which are very loosely organised (you can fly any plane to any destination) to others which are run to emulate more like their real life counterparts. Personally I like to fly for VA which is based on a real airline and trys to fly same / similar routes. It gives a dimension of realism to the Sim, is given a list of routes / flight numbers for a certain aircraft.
@QantasVirtualAirways has given a good list of VAs with different back ground, suggest you check them out and see which of them you fancy! VAs are not for everybody, some people like to fly whatever they fancy…which you still can do with most VAs anyway!