I mostly use the Camaro or the Charger if the tracks have several corners or a wide open:
If it is a mountain track or in general a narrow track , i tend to use the Gulietta , because it does respond faster and you can evade other drivers, if you are playing in playlist mostly.

If i drive in Custom Lobbys ( no collision , i always use the Camaro ; i switch between 2 setups , it is does more or less explain itself, if there are many straights use setup 1 if not use 2 )

As of for Tier 2 , i use mostly 2 Cars ; the Nissan Skyline and the Camaro SS.
The Camaro SS because it drifts around the corner very smoothly.
The Nissan Skyline again has a good start and high stability because of its 4WD , as for Straight Tracks i would recommend it.

As of for Global Challenges and multiple trys for Corners ; drive the Benz , it is almost always the fastest. - The Golf Peformance is really good out of the box, so if you got nothing at the start , drive that one it is a bit similar to the skyline in the end....

// Additional Comment:

Drive what fits you most, that is very important, in my recent matches against other cars and somewhat very good drivers you drive the same time regardless the car, it is about the line and the style.. , you should nevertheless be open for all of the cars here =)

Btw, i am still a Camaro believer :D

For T3 i would recommend 2 Cars:

The Corvette and the Atom , the Corvette does drift very smoothly and has a very high top speed. I updated the Corvette to two setups. The first is more drifty , the second one is more stable ( therefore usable for sprints ).

The Atom is very stable and drives itself like a car in Grid 1 :P

As for Sprint Races i mostly use the Bugatti , as the Koenigsegg tends to spin out rather quickly if you are not too precise with the throttle.

This is video of a battle in the ESL 1 on 1 Ladder, it shows me unfortunatly losing , yes , but it shows how good you can drive in the Tier 2 Cars =)