I have three tomato plants. 2 cherry tomato plants and one regular sized. The cherry tomato ones are doing great, but the other looks like it is dying. It is potted with the same kind of soil, watered at the same time as the others. It is growing, but the leaves are withered and turning brownish. what should I do? is it worth trying to save, or should I just buy another plant and start over again?

Your one affected tomato may be more susceptible to blight or some other malady-and may have come form the nursery with a disease vector. I'd go ahead and get another to add to your collection; that way, if you do lose the original, you have a replacement. If you have to put the new one in the same pot, replace everything, soil and all.