There are 30m more hits on 番茄 in 百度. Search results are pretty much the same for both. Is one version used more in different regions than others?
They both mean tomato,
In mainland China, 西红柿 is used more often while in Taiwan 番茄 is more used.
They are different words used by people from different parts of China, just like aubergine and eggplant for English speakers from different regions. This is very common in Chinese，like potatoes(土豆，洋芋，马铃薯 and more)， pineapples(菠萝，凤梨)...
I would rather say that people from northern China only used the word 西红柿， and people from southern China, as well as Hong Kong, Taiwan, only use 番茄. But of course people understand each other.
An exception is when forming a new word(product name, dishes), 番茄 is often used, despite the regions, like 番茄酱, 番茄鸡蛋汤. Although you can hear 西红柿炒鸡蛋 in north China, that probably only appear in spoken language(or small casual catering). Also， if you look into the words literally, 西红柿 stands for western red Diospyros, and 番茄 for foreign Solanaceae