It's not a question of chance or probability, it's a question of compliance with requirements.
I'm not making a challenge on this, but in principle the requirements are pretty much the same. From most of the cases I know about, some aspects are potentially a liitle more forgiving with Fiance(e) visa than spouse visa.
However there is an advantage for the couple applying for spouse visa in that the spouse being able to work immediately after arrival, with no further expensive visa fees for a couple of years. (Currently)