Some people say that there is a list, others disagree. There is certainly some evidence to support the later. I have a friend who has been waiting for a transfer to his base of choice for 6 months or so. There has been numerous cadets who have got in before him after their line training and more often than not it has not been their first choice of base either. I would tend to agree that if english is not your native tongue then it is often in FR's best interest to send you to somewhere where English is the spoken language. In other situations the airline will send you somewhere that you are needed most. No ifs, buts or maybes. You are told that this is what can happen before you sign the papers, so there is no point in getting upset about it.
I know a few fairly senior guys who have been waiting a relatively long period of time to get where they want. Usually these are the popular bases that have not expanded in the last few years ie. NYO for example. The guy in charge of Flight Ops is a likeable fella, but he has a very tough job and doesn't have a magic wand. We are told that you will eventually get where you want, however patience is the key. There is no point in getting frustrated and venting you anger, especially if you notice a few cadets have jumped into your first choice base before you. We are such a large airline and there is no seniority list, so you have to accept that this can happen. However we are not too large to the point that those heard complaining will end of peeving someone off and in turn never achieve the base of their desire.