I like to refer to some of the following sites to help with this one:
"There is currently no reason to believe that plants experience pain. Plants have no central nervous systems, nerve endings, and brains. The evolutionary explanation is that animals are able to feel pain so that they can use it for self-protection purposes. For example, if you touch something hot and feel pain, you will immediately move, and also learn that you should not touch that item in the future. Since plants cannot move and do not need to learn to avoid certain things, this sensation would be superfluous. From a physiological standpoint, plants are completely different from mammals. Unlike animals' body parts, many perennial plants, fruits, and vegetables can be harvested over and over again without dying.
If you are concerned about the impact of vegetable agriculture on the environment, a vegetarian diet is better for the environment than a meat-based one, since the vast majority of grains and legumes raised today are used as feed for cattle. Rather than eating animals, such as cows, who must consume 16 pounds of vegetation in order to convert them into 1 pound of flesh, you can save many more plants' lives (and destroy less land) by eating vegetables directly."
"It is very possible that plants have sensitivities that we do not yet understand. Because plants do not have nervous systems and cannot run away from predators, it has generally been assumed that they do not experience pain and suffering. Recent scientific evidence suggests that the life of plants is more complex than we once thought. However, we do know that birds, mammals and fish have well-developed nervous systems and pain receptors. Like us, they show pleasure and pain and they present comparable evidence of fear and well-being. Animals cry out in pain, they nurse wounded body parts, and they seek to avoid those who have hurt them in the past.
In order to live, one has to eat. However, when we eat animal products, we consume many more plants indirectly than if we ate those plants directly, because the animals we eat are fed huge quantities of grasses, grains, and seeds to be converted into meat, milk, and eggs. As a vegan (one who eats no animal products) you cause fewer beings to suffer and die for you."
"Most of us would agree that cutting the end off of a carrot and chopping the head off a chicken are not even remotely comparable. But, for argument's sake, if plants do, in fact, have feelings, then we have a moral obligation to be vegan and eat plants directly rather than via nonhuman animals, since it takes far more plant life to feed the animals that end up being consumed by humans than to feed humans who eat plants directly."
In addition to those arguments, I like to point out that plants are treated far more humanely than animals. They get fresh air, sunlight, water, space, and attention. A great many animals raised for food get barely any or none of these things, are often beaten into submission, have their reproductive parts cut off, are branded, crammed into cages, separated from mother at birth or young age or weaned from them way too soon so humans get Moms milk instead, and many animals never see the light of day. We all have to eat something to survive. I would pick the plant over the animal every time for all the above reasons.