Le Meridien is at Central Station (right across the street). Sheraton is at Nord (about a block away). They are equally convenient for the airport. It is the same train - from Central, you need to add a couple of minutes to the ride. I can't quote you a taxi fare, but if the Sheraton @ BRU is out of your budget, a taxi in Brussels will cause you to miss your next mortgage payment, and won't save you much time over the train. The fare from the Sheraton should be less because you are on more "normal" roads by that point.