When I started collecting Heuer, the 70s were the obvious choice for me.
Heuer was maybe at a at the top of the recognition due to branding partnership with Jo Siffert, the Ferrari sponsoring which is a crucial part of Heuer history and strongly counts for me.
As it comes to watches themselves, I love the 70s models due to cases style (Silverstone/Monaco for example) and, above all the color and the finish used for dials and hands (Silverstone again in its fume version for the dial finish and of course 1533G, Montreal/GMTs for colors combination just to name a few)
when I have one of these on my wrist, I know my good mood is guaranteed all day long

Also, as Rich said, case dimension was an issue as it was tough for me to think to wear a watch with a diameter smaller than 40mm

Then I had some opportunities with the 70s Carreras, mainly attracted by the dial finish and again, the link with the sport cars industry,
the 40mm barrier was down but I was remaining a 70s addict

Then a Camaro 7220 NT showed up and I haven't been able to resist to the combination of this dial which has turned chocolate and the contrast made by these so special coral hands.
The case dimension barrer was definitely behind me

Then I've had the opportunity to try Paul's amazing panda Carrera

Fatal try,
I'm grateful to Paul to have let me tried this beauty and I'm not at the same time...;-),
I found out beyond the case itself, the lugs were covering all my (small 18mm) wrist which makes something very special
these tiny Carreras let a simple classy and timeless elegance out,
I'm caught from this starting point and I still love my chunky 70s Heuer like day 1.

Every Heuer has its own attraction to me, including some of the later 11063 cases.
This is a point of evolution we all have in our tastes I suppose as we're moving forward into collecting Heuer, reading threads, admiring contributors pictures and meeting friends.