If I would have to chose what is my favorite rally car, there is only one choice for me: Lancia Delta HF Integrale group A.
In that days (late eighties and first half of nineties) there were two groups of top rally cars: group N and group A.
Group N are cars with smaller modifications: modified suspension, roll bar, safety equipment and some small modification but smaller restrictor on turbo.
Group A cars had all the modifications made by Lancia/Fiat and published in a FIA book called homologation book. Cars were specially modified with bigger turbo restrictor, dog box gearbox, stronger differentials but engine was specially tuned to give nearly 400 bhp. It was not a car, it was beast.
Today these cars cost around 200 000€ if they are in mint condition with FIA gold book (book that says everything about history of the car, every start, every owner etc).
First time I saw it on a rally road alive was in 1993 in Zagreb on Ina Delta Rally (European Rally Championship) and it was amazing to see the flames from the exhaust pipe. Power was enormous. Guys the drove it said: it was like driving a beast.
Lancia has so many World Rally Championship triumphs and it's a shame they will probably never have a rally car again. From what I know they don't exist as a company anymore. That is a real shame.
So the number one rally car of all time for me is a Lancia Delta HF Integrale - RALLYING BEAUTY!!!