Which is better for the Udhiyah: should I slaughter a sheep, or should I share in a cow?

The best sacrificial animals are the camel, then the cow, then the sheep, then one-seventh of a camel, then one-seventh of a cow. The jurists have based this on the Prophet's (peace be upon him) hadith (definition) regarding the virtue of coming early for Friday prayer, where he likened arriving in the first hour to sacrificing a camel, in the second to a cow, and in the third to a ram. The preference for the camel is due to its higher price, greater meat yield, and broader benefit. The Prophet (peace be upon him) might choose something other than the best out of compassion for the Ummah.