If the goal is to win the way the books are written, I'd still take District 2. Lifelong training, the best weapons access in Panem, and a culture that treats the Games as a career path is an enormous head start that no simulation bonus captures. Cato loses the 74th Games to a mutt attack and a plot, not to a lack of skill.
For a survival-themed story, Districts 11 and 12 are appealing choices. That is a role-playing preference, not a claim that they win more often. Their survival bonuses are listed above; this page does not establish the size of any effect on outcomes.
District 7 is another interesting fictional starting point because of its lumber industry and Johanna Mason. Your chosen character, attributes and events can matter more to the story you want to tell than this editorial order.