I have been told by friends that the HE Lamborghini Hurcan is the best car because you get lots of credits and exp from the race. I used my Pagani Huyra BC and one the race and got just over 1.1 million credits from the race and a lot of exp.
If you want the best lap time you can get go with the Centenario or the 918. Now my personal favorite for goliath is the Radical, almost never have to lift off the throttle lol.
Away from my PC for the day so can’t check but how much are Huracan HE going for atm on average?
The most popular car to choose from for the Goliath depends on the amount of grip/handling/downforce it packs(via Porsche 918 Spyder)
Some people prefer the Centenario from the timing you can get, but the Porsche doesn’t require the rear spoiler to even need a good amount of downforce! Seriously, try it ou!
Metalpheonix has Goliath X and S2 world records with Centenario and Zonda respectively on YouTube. Probably the best benchmarks for testing your cars out 
(He claims Regera still fastest for S2 though)
Gurkha is best goliath car, there is no competition.
In FH3 I prefer rides that have AWD. I find the combination of terrain and road surface that the AWD cars suit my style best. For goliath I really like the Lambos.
S2 Class Hairacne Forza Edition off Course Or X Class Centaniario
“Huracan” and “Centanario” are the correctly spelled names. And i agree both are good.