The duo both have odds of 5/2 with Paddy Power that they will take home the crown.
Nadia is the pair's closest competition at 7/2 while Chantelle has odds of 6/1 to win.
Paddy Power spokesperson Sharon McHugh said: "He's got some stiff competition in the form of newly crowned winner Josie, Big Brother 5 winner Nadia and Big Brother's most famous couple Chantelle and Preston but Brian Dowling has everything it takes to be crowned the Ultimate Big Brother champion of all time!"
However, Makosi and Nick are both rated at just 25/1 while John is the outsider with odds of 33/1.
The bookmaker is also offering odds of 8/1 that Chantelle and Preston will become a couple again and 12/1 that they will remarry by the end of 2011.
Ultimate Big Brother continues tonight at 10pm on Channel 4.