I'm wondering what is the easiest way to give a car from one character to another (perhaps on the opposite side of the map). The garages can only be accessed from the owner and cars left without a character nearby may disappear. I remember reading something related to parking lots and car storage but can't recall the details.
When you switch from a character he will generally stay where you left him for a little while. When you switch to a character he will spawn pretty close to his safe house. For Micheal that's usually in Vinewwood, Trevor is Sandy Shores, and Franklin is either Strawberry or Vinewood Hills.
You can use this to your advantage and drive to near the spawn location of the character you want to give the car to, and then switch to the recipient. He can then meet up where you left the previous character and take his car.
Caught on to this trick when I accidentally ran Franklin over with Micheal after leaving the latter standing in the middle of a street.
Edited to add:
Make sure the character you are taking the car from is standing a little ways away. I tried borrowing the Trevor Phillips Industries helicopter, and Trevor didn't like that one bit, pulling Franklin right out of the cockpit.
Theres an easier way, only one condition: -you must at least be to the part in the story where trevor takes over the strip club.
That being said, behind the strip club, kind of by where trevors truck is usally parked there are four or five parking spaces. Namely, two with yellow parking stops. Those are his garage spots, and the fact they are not enclosed lets any character can walk up and take as they please. The car will save there, promise. i put my z type there all the time and dont think twice.
I took all the suggestions and this one works the best 100%. Take the character which has the vehicle you want to switch, lets say Trevor (T). Using him go to a location which is easy to find and close-by to both characters(I prefer the impound). Then using T go to this location with the car and somehow manage to get the car stuck, disabling it from going forward, (being able to reverse is fine). To do this you may jam the car inside the impound green lit garage all the way inside to a corner (hit the car on the wall). KEEP "T" INSIDE THE CAR. Now switch to the character you want to have the car lets say Franklin "F" now take F and drive to the impound with another vehicle. Once there jam his car towards a wall and not inside the garage.( while he tries to forward his car out you can make the switch). Now what you do is switch back to "T" and take the car outside, now get out of the car making sure to park in a park spot near "F" (not right next to"). Now get out of your car and get into another car with "T" (this is important as otherwise T will get back to the same car and drive off") the moment you do switch with "F", now the car you want is free and "T" drove away in another car. Go save immediately as this is a pain in the ass to do again ^.^
After trying several different ways, I eventually passed a car from Michael to Franklin. As Michael, I drove to the strip club after it became Trevor's Safehouse. I parked round the back in the yellow curbed spot and stayed in the car. I then switched to Franklin and drove to Michael's location. As I pulled up, Michael got out of the car and said something to Franklin about forgetting a meeting and walked off. Franklin then got in the car and drove away.