I'm for both, Hourses can do tricks, but I voted cows for these reasons:
Cows can climb steep hills
Cows can carrie over 200 pounds on there backs
cows can pedues milk
Cows can be riden
Cows can pull heavy lodes
Cows can be meat if the need is nessesary(starving people)
cows can swim better then horses
And cows can become mans best friend ^-^!
I'm ganna own a dwarf dairy cow in the next two years just for those reasons. However it would be a close call if this was for goats, cause seped for the 200 pounds on there back, goats can do the same thing XD