JW411 - I do see you argument, but I disagree and I am right at the bottom of a fleet that will see no new joiners on the bottom for a long while.
I get some choice and I have a good lifestyle. The system is transparent inasmuch as I can see who has what and that the rosterers haven't been accepting bottles of whisky to sort someone out.
It works well because the lines are built randomly in the first place. One man's good line is anothers nightmare. The fact that people bid for different things means you don't get stuck with dross all the time.
I have worked on an allocation system before and that was naff.
Having said that, I don't think that the top of the list should get all they want all the time (if there is no movement in the list), so perhaps a little tweak with variable seniority for 3 months a year on static lists would work well. On balance, I would prefer bidline as Carmen is opaque and open to fiddling from bent rosterers (and lets be honest, we have all seen that!).
It also means you cannot put in fiddly requests, like "every thursday night off, but I don't mind if I work in the day" which you CAN do with bidline.