The phrase "big favourite" means that someone or something is liked or preferred by many people or has a high chance of winning or being successful. Full definition
The other big favourite is lots of fun drawing things. (lifeisaparty.ca)
Since independent publishing became a «thing» I barely get the chance to read as I'm also working so hard, but big favourites of mine include Wilbur Smith's A Falcon Flies, Tim Willock's Green River Rising and anything by Michael Crichton. (jfpenn.com)
If anything, the news should only make them even bigger favourites in their match against reeling Newcastle. (caughtoffside.com)