I'd love all three of those, hell even a classic Mini would be lovely, but I don't know the availability of old MInis in LA so I can't comment really. I'd dig a Go-Kart like in San Andreas, the return of some of those Bati Custom style racers from the GTA IV DLC and for kicks, even a modern open wheel racer (F1, Indy).
Not holding much hope out for it as A) what would one of those be doing on the street anyway? and B) can the engine handle the complicated physics involved? Eh, just throwing ideas out there anyway, the vehicles I've seen so far look lovely. (that DB5 lookalike looks tasty.). --- "Don't buy drugs kids, become a rock star and you get em for free!"
Mail truck: http://www.therecycler.com/wp-content/uploads/2012/09/usps-mailing-truck.jpg
I see these EVERYWHERE in real life but they are absent from every GTA even though there are mail boxes in the games. I just think they're neat little trucks anyway, and would love to drive them in game.
Street sweeper: http://www.government-fleet.com/fc_images/articles/GF-45-l.jpg
A big one like this, not like that puny little go-kart one from SA. Bonus points if it actually sweeps.
Fire chief truck: http://www.sewyco-fc.org/images/1851.jpg
Sleeping Dogs had a Smart Car knockoff called the Emu. --- HOLY ****! What is this? Forged in Gods very flames! Do mine eyes tell me lies? A new Elder Scrolls game? Time is nigh, I must fly, Venture forth on my quest!