Answer: north but a slight edge.
Explanation:
In case you need a recap here are the 5 main points of the compromise of 1850:
1. california is a free state
2. new mexico and utah could pick whether to legalize slavery
3. mexican cessional territories could also pick
4. enforced stronger fugitive slave laws
5. abolition of slave trade in DC
from the beginning, the Missouri compromise was like putting a small bandage on a huge wound. didn't really help the antislavery or slaveowners settle the issue of what would be legal across the whole country, it instead promoted the south and the north to stay separated. the mexican-american war was waged by the federal government, and the outcome of the war didn't help solve sectional tensions either; it made it worse. ok yeah the north got another free state, along with the freedom of the capital that abolitionists worked very hard for, but the south was allowed to keep their business to themselves and who knows? the new territories in the west/midwest might permit slavery after all! so this is why for the most part the compromise was a pretty split deal, BUT...
the reason why i think the north had the slightest edge in this case is because they didn't strictly enforce the fugitive slave laws! you can see that with harriet tubman and her underground railroad, and in addition, reformers such as frederick douglass and harriet beecher stowe only continued to preach for antislavery, and it did lead to eventual changes. not only that, the settlers who moved to the territories in the west/midwest were families looking for new work opportunities/open up businesses (aligned with free soil ideals) so of course, they didn't want slaves because it would, again, ruin their chances of making profit. so you can prob guess what they voted for. and there you have it.
cheers,
a fellow apusher