Hi Devonrob...
Sorry to tell you this but if you are last off then you can look forward to a much longer wait at immigration in ANU than half an hour. If you are at the back of just one 747 you can look forward to an hour or more. However if you arrive on a Saturday then there are also BA, AA, BWIA and BMI flights on the ground and the place will be packed.
When you get off the flight try and speed-walk past as many people as you can before you get to the immigration hall as each person in front of you is realisticly a two to five minute wait.
Now then...when you get to the immigration hall there will be some queues forming, possibly out of the door. Walk to the right of these until you come to the far right two lanes. Dont just join the first line you see, there are actually six to eight lanes in the hall. If people are queing out of the door of the hall they have unwittingly joined the first four lanes and are unaware that there are additional lanes in use inside the hall.
The extreme right hand lane is for Antiguan and Caricom citizens. Use the lane immediately to the left of this lane (so the last but one lane on the right of the room) if you can.
The reason for that is that the caricom citizens line moves fastest, once they have processed those people they will pull people from the next line, so instead of having 2 immigration officers per line you now have four.
If you are travelling with children in a push chair they will also put you into this lane (most of the time).
When you finally get into the customs area of the room your bags will most likely have been pulled off the carousel and will be on the floor so its like an easter egg hunt. Try to keep some small US dollar bills or five EC bills and use a red cap to get your bags through customs as those guys tend to get you through customs a little quicker.
Needless to say if the immigration hall is quiet and customs is quiet then do as you wish but if the place is packed this is the way I have found will get you through the fastest.