Well Wasim and Waqar certainly have a case, but I would rate Bracken ahead of both Pollock and Donald. Maybe that's because I'm an Australian, but I don't rate the South Africans as highly as most others. Pollock was quite tight, but still managed a worse average and Strike rate than Bracken. Pollock and Donald also played in more bowler-friendly playing conditions than did Bracken.
Just because a player is fast and can swing the ball doesn't necessarily make them a better ODI bowler than another. Bracken is so versatile you can bring him on at any time and he'll make an impact. He has a fantastic strike rate, average and economy. In this series he's been a class above anyone else playing.
EDIT: I have just realised that your comments are truly praising Bracken. That you have to look at bowlers of the calibre of these four to find anyone who is arguably better, it really proves my point.
This would be Bracken's defining moment in ODI cricket IMO:
Cricinfo - 5th ODI: South Africa v Australia at Johannesburg, Mar 12, 2006