what scale automobiles should i use for o scale layout

Last year I bought the MTH packet of unpainted figures for $25 I think.  Most are sitting.  I painted them up and populated all of my 'moving' cars.  What a huge improvement, especially since many of these cars are convertibles.

Their arms are not extended, but unless one looks real close no one seems to notice.  I tried 'adjustable' Circus Craft (?) ones but they were too big for the 1:43 car seats.

For the standing figures I lopped of their legs and glued them in a seat - this worked well for sedans and trucks where you don't really see inside anyways.

BTW: 3 years ago I bought the same packet of figures and populated my passenger train.  Again, huge improvement.

- walt