Here's the question - Are you going to project this image through an analque projector (vs print vs digital projection).
Tonal repsonse aside, if you have a projector and will display it that way, go Velvia (Slide/Chrom/E6). If you don't have access to that, I say go for Ektar. It is still a very saturated colourful film, is scans very well, and it prints beautifully.
The difference between Ektar and Pro 400H is noticible.
If people are going to be visible in the photo, I'd steer clear of Velvia (I just find people look weird in it). Ektar isn't bad, Porta or Pro 400H are best for people (but the colours are definitely muted, so if the focus is the colour of the car, go for Ektar).
While not on the list, probably because it is a lowly consumer grade film, you should try a roll of Fuji Superia 200/400 if you haven't. I find it is more saturated than Pro 400H and makes a nice midway between 400H and Ektar. It enlarges nicely up to 11x14 print. I ran through a dozen rolls last spring while on a trip through Alberta, the rockies, and BC. I shot Pro 400H, Agfa Digibase 200 E6, Superia 400, Porta 400, and Ektar. I was disappointed with the 400H because in similar shots I always prefered the Superia 400 print.