Anyone besides Literally Rauner with a D next to his name (Pritzker) would be favored.
With Pritzker its pure tossup.
Pritzker will win by 5 points, all our IL governors' races end up being that way Blago won by 6 and Rauner won by 5. And Pritzker will win 50-45%
I really want to caution against this line of thinking. Rauner's initial election was the product of a confluence of Illinois-specific factors (the perception that Mike Madigan runs the state, the state's steadily worsening fiscal condition, loss of jobs and emigration resulting from said fiscal condition, etc.). All of these pushed enough voters to elect a moderate Republican to push back against the perceived Illinois machine. These factors are still present and any perception that Pritzker and Madigan are aligned would be a hindrance to the voters in Illinois who, for instance, cast a ballot for Obama, then Rauner, then HRC in three successive elections.
Today is the final day of the Illinois legislative session and the House is taking up a compromise bill between the Governor and the State Senate. Any whiff that Madigan is blocking this compromise / "grand bargain" will hurt any D backed by Madigan in the Governor's race.
Not because voters really pay that close of attention, but because Gov Rauner will spend every day on the campaign trail and every tv ad saying that he and the State Senate had a deal to fund the state government, but the Pritzker-Madigan machine blocked it. And it'll play. Exceedingly well. Especially in the suburbs.
A Kennedy or Biss would be able to distance themselves and could sell themselves to voters as a left of center choice (ideologically fits the state) who wouldn't be beholden to Madigan (independent voice).
In short, "Generic D" would be favored against Rauner, but Pritzker is hardly "Generic D."