Dexter... by far. Heath had the right strengths to match up well against his chief competition: Jay, Kai and Rami. Heath had the better back and back double biceps pose. Heath had better arms but Dexters arms were pretty good. Heath's arms and back were his strongest points that won him shows over Jay, Kai and Rami. At damn near 50 years old Dexter very nearly beat Heath.
I would much rather have better abs and serratus than a back, but the modern era values a good back, "Sandows are won from the back etc...", while most guys today have blown out waist lines, distention and massive hernias/ gaps in the abdominal and no one cares.
Dexter was better balanced, tighter abs and won 3 times as many titles as Heath. Heath won a couple of pro shows then went on his Olympia run. Heath had like 8 or 9 first place finishes, Dexter had 26 or 27 pro victories including an Olympia.