Trackwork rider Steve O'Halloran can't fault star mare More Joyous who is chasing her biggest career win in the $2 million Doncaster Mile.

Trackwork rider Steve O'Halloran has worked with many top-class horses prepared by Gai Waterhouse but Doncaster favourite More Joyous sits at the top of the tree.

"She's on top, definitely," O'Halloran said.

"She's probably the best out of the lot of them to me."

O'Halloran, who has worked for Waterhouse for eight years, rides More Joyous in trackwork most days having done likewise with a number of other high-profile horses.

"The first horse when I came over (from Ireland) was Grand Armee," he said.

"Then I had a lot to do with Dance Hero leading into the Golden Slipper (2004).

"Fashions Afield, Aqua D'Amore, Meurice. Then you've got the likes of Sebring, and also Pierro this year.

"There's been a lot of good horses through the place since I arrived."

While O'Halloran gets to partner More Joyous in trackwork during the week, on race day that tasks shifts to champion jockey Nash Rawiller.

More Joyous has returned this preparation with victories in the Group Two Canterbury Stakes and then the Group One Queen Of The Turf Stakes, her sixth win at the elite level.

"She's going fantastic this preparation," O'Halloran said.

"She's ticking every box leading into the Doncaster.

"She worked on the course proper (on Tuesday morning) and worked as good as she ever has, so she's on target for Saturday."

More Joyous has the task ahead in the Doncaster as she will have to carry 57.5kg and give weight to all but Rangirangdoo (58kg).

The mare failed in last year's Doncaster on a heavy track and rain has continued to fall in Sydney this week which has put a question mark on whether she will take her place.

"The 57-1/2 kilos, she'll handle that no problem," O'Halloran said, but admitted a bog track would pose a concern.

"That's the only thing. If it's a heavy track then maybe you'd have your doubts. But I'm rapt with the way she's doing."

More Joyous has long been a stable star having competed at the top level during the past four autumn carnivals.

"I've been here over eight years now and I've sort of been on her (More Joyous) since she was a yearling," O'Halloran said.

"She's a bit more chilled out now than when she was a younger horse. She's a sensational horse.

"You wake up in the morning and you come to work. You might be having a bad day and then Gai says `get up on More Joyous'.

"When you have a lot to do with her it's very fulfilling when she does go to the races and win the way we know she can win. When she puts her best foot forward she's very tough to beat."

O'Halloran will actually strap a rival runner in Saturday's Doncaster, More Joyous' stablemate Niagara.

"Dave Meijer looks after More Joyous so he'll be strapping her and I'll be strapping Niagara," he said.

"But I'll still cheer for More Joyous as well."