[sexton626]

Originally Posted by henk4

size is actually not too important, but 1/24 is the most common. What does matter in car building, contrary to airplanes, is being able to do a proper paint job of the body, taking ample time of cleaning it, removing mold lines, grounding/sanding and finally putting on the real paint, in several thin layers and then again sanding and polishing until you get a deep shine with no orange peel.
Try this first on cheap models of curbside kits.

More important than scale is to choose something that really interests you. If you're interested in modern street machines, 1/24 is best represented. For modern F1, 1/20 would be the choice. By far the scale with the most choices is 1/43.
I disagree with henk4 about paint not mattering on airplanes tho! It's true that while the technique for gloss paint is somewhat different than for flat paint the key to a successful model is a smooth, error free finish.