Best way to redeem ticket for car?
Tickets are random.
You can maybe use a marketplace forum (like on gtplanet.net for example) to trade it with another car you don't have, or you can use non-reversable tuning on one of them (weight red, engine tune stage, regidity), then compare performances.
You could backup your save to a memory stick before opening the ticket. Then open it from the save on you HDD. If not happy with the gift, then copy the backup back to the HDD and try again.
A lot of work though.. and might be considered cheating ;D
But at least its a posibility.