If you asked this a couple years ago - you'd have been told FIRST GEN but now there are several manufacturers doing killer SECOND GEN stuff.... Having never built a 2nd gen car - personally - I can't speak from experience - but I can tell you that right out of the box from the factory the 2nd gen stuff was far superior to the 1st. Now - with all the dev work and sub frames etc for 1st gen - that difference has probably been erased.
A 2nd gen donor should be less than the equivalent 69 first gen... and might have less rust issues. But given that you're in Westchester, NY (I lived in Scarsdale for a few years) RUST is an east coast issue no matter what...
If I was on a budget - I might try to find a 2nd gen donor... but If I wanted resale value and looks - then I'd ONLY build a 69....
So nobody is going to answer your question to your satisfaction... only you can do that. It's a tough call because the body style is so personal.
Since the question was 2nd gen vs. 3rd gen, between those two:2nd gen all the way, with my personal preference being the 70-72 with RS nose.
__________________
______________________________________________
1969 Camaro/ Tom Nelson TT 434 / Wayne Due C5 / DSE QLink / and a bunch of other stuff...
That is because there is no arguement for a third gen......
When they stuffed a 4cyl in a Camaro I was done with that entire generation with the exception of the IROC/Z28 there was not much offered by that series.