I voted for the Porsche and the BMW, because they gave the closest racing in my opinion, which is always what I prefer. One way you can look at the closeness of the racing is the "Busiest" stat for the last 4 races, which shows the smallest average gap to neighbouring cars, front and back.
The smallest average gaps were:
BMW - 1.90 secs
Porsche - 2.15 secs
Lotus - 3.61 secs
KTM - 6.40 secs
I preferred the Porsche because it gave close racing, but wasn't quite as easy as the BMW. It was easier for those around me to make mistakes, which lead to more position changes. Also, the tyres actually go off in the Porsche, whereas the BMW and Lotus tyres are much harder wearing without much degredation over the course of the race.