What makes a BMW unique is its balanced driving dynamics; an active air ventilation system is likely a feature that may also be available on an Audi. You should check with the dealer.
One advantage of an Audi, if your choice is so-equipped, is the Quattro all-wheel drive system. This drivetrain can aid in driving the vehicle in a variety of conditions, including inclement weather. Otherwise, a standard 2 wheel drive A4 will be front wheel drive whereas a BMW 3 series is rear wheel drive.
Mechanical reliability is a about average if not a tad bit lower, however, which is actually typical of most premium German automobiles.
Now, this doesn't mean that Audi, BMW and Mercedes-Benz makes low quality cars, but you need to understand that premium luxury and performance cars tend to require more attention in regards to service and repair because of the extra level of complexity these cars will have in design and build. The less simple a design, the more that can go wrong with it. In short, if you want a premium model Audi, do not expect Honda-like reliability. The best you can do to help ensure reliability is to keep the car maintained according to the vehicle's service guidelines and not to make a bad habit out of driving aggressively as such driving behavior is going to be hard on the car and will hasten wear on the parts of the vehicle, requiring more frequent service and repair (not to mention increasing the risk of a crash).
For your first car, are you sure you'd want to get an S-line?
If you are going to get your first license, a powerful car meant for performance is not exactly a good first choice; I mean no disrespect but young age and inexperience can allow some foolish choices to be made and, when driving is concerned, all it takes is just one mistake to create permanent tragedy that you will have to live with for the rest of your life.
Let's face it: driving can be a dangerous activity and the higher likelihood of mistakes from young age and inexperience can be compounded by complacency; if you are used to driving being routine, you may make yourself think that the potential risks will not happen to you, which can encourage you to deliberately make more reckless choices.
Your automobile insurance will reflect those realities accordingly with higher coverage rates and, as you may already know, reliable coverage from auto insurance is compulsory for licensed Florida drivers.
For your first vehicle, if you insist on a brand new Audi and actually have the means to get it, I'd recommend a base level A3 or a base level A4. Otherwise, I'd recommend looking at compact or midsize offerings from Volkswagen, Honda, Mazda or Ford.
Do not forget, the primary purpose of driving on a public roadway is to get to your destination safely.