I am against needless animal suffering, such as factory farming, so I should probably be against bullfighting. But it offers an interesting test case for a purely utilitarian response to animal cruelty. Basically, utilitarians believe that an action is wrong if it leads to a net decrease in happiness. So, something like factory farming is clearly wrong because the amount of suffering produced during the lifetime of the animals raised in awful conditions outweighs any pleasure meat-eaters might get that they couldn't get from eating other food. (This is oversimplified because there are other considerations, like the environmental damage from factory farming.)
OK, but what about bullfighting? One might argue that the bulls are raised in relatively good conditions and then suffer pretty badly for some time, but that the suffering is outweighed by the happiness experienced by the spectators. Again, oversimplified--e.g., perhaps the spectators could easily find substitute sources of happiness that do not require animal cruelty--but it's an interesting case.
Of course, one might think that these sorts of calculations and conclusions show why utilitarianism is a problematic moral theory. There are certainly other arguments one might offer for why bullfighting is wrong. And it's not clear exactly what the arguments would be for why bullfighting should be preserved, except for tradition.