In reply to daWalt:
The Airlink 100 bus is also marginally quicker than the tram - at least according to its timetable (but see below) - and IIRC the walk to the check-in desks is shorter! The bus is rather more comfortable than the tram as well; it's always a nice surprise to find yourself on an ex-Airlink 100 bus when you were expecting the usual, rather shoogly general service bus (unless it's busy, in which case the reduce seating capacity becomes apparent). The internal layout of the Airlink 100 buses is also specifically designed for airport passengers, with generous provision for luggage, whereas the tram is a bit of a compromise between city centre/commuting passengers and airport users. Both Airlink bus and tram can be busy during peak hours, but the Airlink bus less so because it stops less frequently and AIUI isn't meant to set down at the limited number of intermediate stops on its route - its job is to take people to the airport.
About the only potential downside to the Airlink bus is that it can get caught up in traffic congestion. There plenty of bus lanes on the route but they don't help much if e.g. there is a throughput-reducing incident at a particular junction.
So, as long as you're not tight on time to make your flight, I'd say the bus is the preferable option. Unless, of course, you particularly enjoy riding on trams.