Wait. What?
this reminds me of a trick question. Which disease is worse? Bubonic Plague or Small Pox.
On my vegan journey, my first step was to stop buying milk. Not all dairy. just milk. that was the biggest percentage of my dairy consumption. And it was about the easiest thing to do. Just buy soy milk instead. I was also motivated by an article in my local paper. It turns out that at the time PETA was suing the California Dairy Board for their Happy Cow Ad Campaign: False advertising. BTW, they lost. But in the meantime, I became interested and stopped drinking milk.
Also when analyzing this kind of stuff you need to not just consider carbon but all the greenhouse gasses (GHG). Cows and chicken produce other greenhouse gasses. And some of them, even if produced in smaller amounts have very large consequences in global warming and also persist in the atmosphere longer. I'm talking about methane mostly.
I did find one source that had some numbers.
" Breaking down the 4.2 percent EPA figure for livestock by animal species shows the following contributors: beef cattle, 2.2 percent; dairy cattle, 1.37 percent; swine, 0.47 percent; poultry, 0.08 percent; sheep, 0.03 percent; goats, 0.01 percent and other (horses, etc.) 0.04 percent."
https://caes.ucdavis.edu/news/articles/2016/04/livestock-and-climate-change-facts-and-fiction
This particular study I don't' quite like, tho. I think the 4.2 percent number is a gross underestimation. to give the authors some credit they do mention the higher number that I subscribe to. The scientists who came up with the 18 - 51% number take into account the fuel used to transport food to the livestock and then the fuel used to transport the livestock to market. They even include the GHG produced in growing the food for the livestock. How the scientists account for these things is why the range is so large. But still 4.2%??
Give it a day or two, I'm sure Forest Nymph will have something to contribute to this thread.