well I have seen owned and worked on all 3 (67-89)
fords twin I beam was worse problem here in the country (bushing wore out) second was "brain box"

chevy's seem to rust more than the fords did and the starter was the worse problem with them.... 305 ate cams liek candy but the ol 350 was good motor

dodge hmmmmmmmmmmmmmmmmmmmmmmmmmmm before the cummins it was looking gloom for mopar...
eletrical problems and tranny's was Dodge biggest problems on the years listed above

in my area you see

a tie between ford and chevy and you RARLEY see a dodge in the years listed above....

now if you get into the newer models

ford and dodge dominate in the 4x4 and the deisel market chevy new desiel is starting to catch on

in the gasser 4x4 and 2wd model its a dog fight between ford and chevy..

in the small trucks FORD all the way all you see are rangers or explorers then some blazer and very few durango's

the one thing you don't see around here is the chevy 6.2 or 6.5 most poeple switch to the ford 6.9-7.3 lots of them running around here...the old box style dodge with cummings is rare too but the newer one are getting common