Hi Bilal, very interesting question and I assure you, it isn't easy to provide a fully satisfactory answer.
Unlikely as other car forums, we're very proud of our users that they have a much broader view of sports cars and aren't focused (as some "fanatics") on one brand only.
I love Porsche, I love AMG and I love Ferrari. All three are completely different cars and it is very difficult to compare them.
Let me put it this way:
1. AMG: very nice, refined and very very poweful cars with a high quality standard. These are cars for power mongers and understatement lovers, the perfect Autobahn racers. Unfortunately when it comes to the heart, AMG isn't my favorite. They lack traction, they lack emotion and they maybe are too perfect in a certain way.
For a 18 year old, a AMG Mercedes is a "no go".
2. Porsche: if you want a real driving machine, Porsche it is. Drive a Porsche shortly after you drove a AMG Mercedes and you find yourself in a different world. The steering is more direct and responsive, the suspension is one of the best in the world and you can actually "feel" the road in a Porsche, something which makes it really unique. The rear engine design provides traction without limits and the flat six engine sound is something spectacular, especially with Porsche's own sport exhaust. The design could be a bit more spectacular but it is actually timeless.
3. Ferrari: well, something for the brain and something for the heart, you can't do anything wrong with a Ferrari.
Some people find it's design to flashy and it surely isn't the car you want to take to your university (some of your profs might put an eye on you...
) but for a 18 year old, definetely THE
womanizer, the coolest thing to own.
Performance is great, drive feel is almost the same as on a Porsche but it needs a lot of money for maintenance and a good mechanic is a vital thing you need on a Ferrari.
Personally I think that a Porsche is the perfect car for a 18 year old (not too flashy, very sporty) but I have to confess that being a father, I'd never buy my kid a Porsche, Ferrari or even a AMG Mercedes at age 18.
When I remember my driving abilities (and my driving "behaviour
) at age 18, I feel very very bad.
So maybe you're more mature than I was at your age but you definetely should be very careful with such cars. Each of them is a real weapon and weapons need a lot of care and experience.
Good luck with your decision.