Which car should I get and why? First car btw?
Choose the Honda Civic.
Even today, just having any car on campus will be ++ social points, even for less flashy Civic... & you want to be liked for yourself, not your car.
The Honda Civic will cost much less to operate and maintain than the Mustang. GPM is likely much more favorable for the Civic than the Mustang, with any of the typical engine/trans packages [This question should include your engine/trans info.]
Your auto insurance is likely to be MUCH LESS for Civic than Mustang [Mustang rated for more/higher claims. Driver < 25, esp <21, rated even worse with Mustang]. And... (-drum roll-) ... the #1 reason. As totally her own idea, my daughter just sold her pride & joy, dealer-rated as 'primo,' 40th Anniversary Special Edition (black) Ford Mustang ... and bought a Honda!
[Absolutely true! Of course, she has paid her own way for a while. AND she drove an old Saturn during college.]
And, now the hidden reason -- Your choice and reasoning will impress your family in the right ways. As you move farther apart, such things have value that cannot be quantified.