I've always liked the early trucks, parts are plenteful and CHEAP!, and so damn easy to work on! the 68-72's are very smooth and clean for their year, but the 73-87's have lots of interchange ability!.
I personally have a truck I've been working on. It's a 76 GMC 1/2 ton, short box, fleetside, with a 350 chev with a feul injected tunnel ram, 5 speed, 9" ford rear,4 wheel disc, swaybars, lowered 9" & 12" (spindles, springs, dearch, shackles, & 3 1/2" body channel), '86 front clip with a phantom billet grill, all rolling on a set of 17" boyds wheels.
My daily driver is a 91 GMC Sierra ST with the factory 305 V8 auto drive train with custom body/ piant, lowered, 17" Boyds and a kicken stereo, and I love it since its the last of those trucks before the started going electronic everything, parts are still cheap and easy to fix and maintain.
Tough dicision