the old cheiftain range was 1:56, ( also sloppy jallopy and bolt action). a 28mm fig on a base will look tall compared to the vehicle unless the vehicle is based.
the HLBS modern range is 1:48 and modern 28s ( read larger) on bases look fine next to them, but will look small next to a based 1:48 fig or 1:48 vehicle.
1:43 look massive next to most figs, based or not ( from using an airfix land rover next to mongrel, blacktree, and gripping beast 80s brits)
a lot of this is due to many people seing vehicles as being larger than they are.
with a lot of them though, if you use 1 scale for each vehicle ( or better 1 scale and make for all) it wont stand out too much to the eye, but 2 vehicles from differnt sources will pull the eye to the wrongness if the size differance if more than a few mm
hope that helps...