Petrol cars are more common amongst young students due to low-priced fuel costs and engine repair costs. Though if you do commute to uni hence travel a lot of miles and plan to own the car for a while, then a diesel car may cost you less in the long run. Choose Diesel if you do at least 10k miles per year (usually if you commute to uni from home) or if you plan to own the car for a long time- their general automotive health lasts longer than petrol cars!
Petrol is the slightly cheaper fuel option at the pump. The fuel choice is ideal for a short-term car that you perhaps plan on swapping once you are working full-time, or if your journeys tend to be short most of the time.